How to make pictures look better like on tumblr?

For example:

They just look so HD and really good quality. How can I edit my photos like that? I have an nikon L120 so the quality isn't that bad but I want them looking like that^^^.

You have a decent camera, maybe not great, but do able. Those pictures are not very special, nor do they have any real "HD" quality to them. To get pictures like that you need to have good (1) composition: how the subjects in the photo are arranged to be pleasing to the eye. Google "rule of thirds" (2) Lighting: the lighting can't be too harsh or over-the-top, it has to be just right to convey what you want in the photo. The things you can do in post editing in programs like Google Picasa or Adobe Photoshop are adjust contrast to make things stand out by adjusting the lighting, adjust the color saturation, change the colors, crop your images, etc… But the main thing that gets a good photo is the camera and the person behind it, there's not a lot you can do in editing to make it a good picture, you can only improve it. My advice to getting good photos: (1) learn photography: take free courses online. (2) get a better camera like a dSLR (3) take pictures of what you like first and foremost, do post processing only to bring out what you saw.