I do amateur photography mostly on friends, and my pictures come out blurry when I send them across. I have a few (well more) questions?

I shoot on the Nikon D3300 with the lens that comes with it.
1)I take pictures as RAW+JPEG because you can't send images across as RAW, so how do professional photographers take loads pictures edit them as RAW and maintain the quality? Like do they convert each picture one by one?
1a) How do professional photographers send the pictures?
2) The JPEG pictures look fine on my laptop but when I send them on whatsapp or something like that and they post the picture on instagram the quality looks worse. (My ISO is usually 100/200)
3)I use GIMP to edit, when I save the photos from RAW and export to save it as JPEG does that decrease the quality?
Sorry about all the questions I just need to learn how to keep up the quality

Professionals don't always shoot RAW. Those who don't do so usually because of the additional processing time. Say, for example, you're shooting the World Series. You have a critical deadline that prevents you from converting all of your RAW files to DNG, then edit them, and then convert them to JPEG. You simply don't have the luxury of shooting RAW. Others don't shoot RAW for similar reasons. They understand that time is money, and the additional time that they would have to spend in front of a computer is time that they can't be promoting their business or making money by photographing. So as a business decision, they shoot JPEGs. But if time isn't a constraint, and the ability to process RAW files in ways not possible with a JPEG outweighs the additional time involved, then a pro will shoot RAW.

Once the file has been edited, pros will send their work to printers or printing companies, or to their clients as JPEGs in the sRGB color space. It's critical that the image files be in the sRGB color space because this is the color space that all web browsers are designed to display. Color spaces can be looked at as being like a painter's pallet. Each color space (e.g. SRGB, Adobe1998) is comprised of specific colors. Not all color spaces have the same colors. For example, there are a lot of colors that are within Adobe1998 that are not in sRGB. So if your image is using colors in the Adobe1998 color space and you try to view it with a web browser which uses sRGB, the web browser can't display all of the colors in the file. When a browser comes across a color that it doesn't have, the browser has to make a guess as to which color to use in its stead. This leads to files looking nothing like the original did when processed in Photoshop or Lightroom, or any photo-editing app for that matter.

You say "… The quality looks worse." The term "quality" is a very vague term and can mean many different things. If you're using the sRGB color space, then the usual culprit for bad quality is the site that you're posting your images to. For example, every single social media site from Facebook, to Twitter to even Flickr all edit incoming images to fit their required resolution and file size. This means that if you do not edit your resolution to the size that they require and choose the correct file compression that reduces the overall file size on disk to their requirements, then they will do it for you. Often this leads to blurry images because these sites are not using good-quality algorithms to reduce the resolution or to compress the file. You will almost always get far superior results if you edit the photo using a good quality image editor like Photoshop, PhaseOne, OnOne, GIMP and the like as opposed to letting the website edit your images for you.

Your D3300 shoots 12-bit RAW files which means that the files have a total of 4,096 tones (2^12 = 4,096) from pure black to pure black per RGB channel. When you convert the files to 8-bit JPEGs, the number of tones drops to just 256 (2^8 = 256). That means that you're deleting 94% of the data that was in the original RAW file. Now while this probably sounds like a horrible thing to do to a file, it's actually not so bad, just as long as you keep the compression to a minimum. When a file is compressed, colors of a specific range are all replaced with a single color. This means that there are far fewer shades of that color which can often, but not always, be seen as color banding in areas of solid colors such as blue sky. If you keep the compression to a bare minimum, there will still be enough tonality in the image so as to not see color banding. This is one of the reasons why you need to edit your images to fit the requirements of social media sites and not let them do the editing for you.

Not all monitors are calibrated the same. For this reason, an image will look different on your smartphone, tablet and computer monitor. All three devices do not have monitors that are calibrated. In fact, most monitors are way too bright right out of the box which causes people to edit images in a way that makes them too dark. You can mitigate this problem by purchasing a color calibration tool such as a Spyder or Color Munki.

If you do these steps, then the quality of what you see on your monitor when editing the images should be the same when you open the image on a web browser on the same computer.

I expect that whatsapp is messing with the quality and then instagram is messing even further. And there may be filters your friends are using. They both compress photos (removing quality) so that they have a small filesize so you don't use all your data downloading them. They shouldn't be blurry to any great extent though. (Note that blurry usually refers to when there's motion of the camera or subject, what you are seeing is either softness or focus issues)

If you want to maintain quality as much as you can then save them on a file hosting site, e.g. Flickr and send the link so they can be downloaded.

If you are only doing this for social media then you are probably wasting your time with RAW unless you have a particular need to change the white balance or play with the extremes of the exposure. JPG is pretty good in most circumstances

Saving to JPG will reduce quality a bit but this will only really be noticeable full size. What are your save settings in GIMP? Are you saving at a reasonable size (1024 x 683 or something) at the highest quality?

RAW is essential if you do heavy image manipulation. Otherwise, JPEG suits fine to most people. To the uninitiated, JPEG photos look no different from converted RAW photos anyway. In the end, most pros upload as JPEG since that is what most internet sites and viewers require.

The problem with uploading photos to social media sites however is that these sites (all of them) degrade photo quality to make file sizes small enough for fast transmission through the internet. Whatever you do, they always make it worse. The best you can do is to ensure you upload only photos with a high exposure quality. That way when the social internet site degrades photo quality, your photo will come out as decent at best. Hint - it's not just ISO. It's everything. You have to nail exposure right on the spot.

GIMP is all right. I use it too. When saving to JPEG, make sure you save to 100% quality. Do not depend on software for your lack of shooting skill or laziness. Get it right in-camera. I usually know what I want beforehand when taking a shot so I only process the photos in the computer to fine tune exposure (contrast, gamma, saturation) and to put additional graphics (logos, text, etc. If required - I don't watermark).

Fastest way to increase followers

When converting to raw choose the best setting.
Convert the images yourself to the size that Instagram likes. That way IG doesn't have to convert them again and cause extra blurryness. Eg 1080px in width by 1080px in height.