Your camera may have slightly different letters to denote the different shooting modes, but they are basically this: Aperture, Manual, Speed, Program or Green (point and shoot and hope for the best).
In a nutshell, "A" tells the camera that you will decide what aperture to use and the camera will do the rest, same for S for speed - you pick the speed and the camera picks the aperture (separate and apart from ISO. Usually.) I don't know what "P" does - I never use it.
In Manual you pick everything which means you have to understand how aperture, speed and ISO are all going to come together to make a good exposure. And that takes some practice.
I had my camera for two years before I moved off of green, and then I had to force myself. I was getting good shots on green, but when I made the effort to learn how to control my camera, I was able to do so much more creatively. I got a zillion really bad shots in the process. At this point I'm fairly comfortable with Aperture mode because I love to take pics of people. Who are not moving fast. And flowers. Because they don't run away.
This shot was taken in Aperture mode. Would have never gotten it on green.
Here's a link to an interesting list of why you want to learn to shoot in manual that I found to be very helpful.
So what mode are you shooting in? And what kinds of things do you like to photograph? Show me your best shot!