Manual auto focus tips on DSLR?

Hi. I just bought Nikon AF NIKKOR 50mm f/1.8D Lens for my Nikon D3100
When I got it I realized that it doesn't auto focus heh. My first camera, so…
I now understand that I should've bought AF-S lens which is twice the price. I could send it back, but I'm going on a trip so I don't have a time.
I also read that there are some people who use ONLY manual lenses on their DSLR's because they think it's even better, but why exactly?
So could you, please, guide me through this. Tell me everything that a person should know about manual focusing and what makes it easier. Parallel to this I'm also reading articles about manual focusing, but rare and subjective tips would be in a gold's value. Give me everything you got.

Added (1). UPD: Also I can't seem to change Aperture. It tells me to lock on 22(highest number).Is it possible to change that?

Added (2). UPD2: I understood how to change aperture, thanks.

Manual focus on your camera is possible, but not easy. The viewfinder is small and dark, making it difficult to actually see what you have in focus. Practice is the best advice for learning how.

Locking the aperture ring allows the camera to control the aperture automatically. If you don't want that automatic control, you just set the aperture ring to whatever suits your purpose and shoot. Leaving it locked is not really an issue, as you can change the aperture using the control dial just as easily, without having to look at the lens to set it.

I have a D3100, and when focus is achieved, you will see a small green light at the bottom left of your viewfinder. Since your new lens is MF, you can use the arrow keypad to set a point of focus. Once you choose that, turn the focus ring slowly left or right, until that green indicator light appears. For the best MF, you need good eye sight and your viewfinder needs to be in focus to your eyes. Practice makes perfect.

Love my 50mm 1.8d

To change the aperture, first you have to lock the aperture ring to 22 (BTW, 22 is the smallest f-stop, 1.8 is the max.)

To lock it, you turn the aperture ring until the number 22 lines up with the white dot. Then you push the switch down until it's in line with the other red dot.

To set the aperture, you just go to your cameras menu and change it through that.