There are at least three things that come to mind, one of which had to do with installing mods. I had watched video after video on how to install the Mo'Creatures mod, but without any luck. I later figured out (days or weeks later,) that I had to be on the right version of Minecraft to install it. Another one of the reasons had to do with installing a map called Desert Oasis. When I downloaded it, the map that I had to put into the saves folder was inside another folder of a similar name, so when I tried to play the map on Singleplayer mode, I couldn't find it. Good times.