To explain the 3's I think it might be easiest to give you a quick, short theory lesson.
1. The black notes with stems are called quarter notes, which means each one usually gets one beat.
2. When there are three quarter notes with a 3 above them, that means they should be evenly spaced out to take up two beats instead of three. In other words, they are squeezed together a little bit, time-wise, so three of them will fit in the same amount of time that usually only contains two of them. It's called a "triplet". Instead of each one getting one beat, each one gets 2/3 of a beat.
I hope this is enough information--but not too much--to make it sort of understandable??