Look at the image of the music staff sheet below. There are 5 staffs, or staves, and each staff is made up of 5 horizontal bar lines.
On the 1st staff, at the left end, I've circled one repeat sign, made up of 2 vertical lines and a pair of dots on the right side. On the 3rd staff, at the right end, I've circled a 2nd repeat sign, where the dots are on the left side of the 2 vertical lines. When you encounter the first repeat sign, that becomes your signal to keep in mind that, sometime up ahead, you are going to get to another one, this time with the dots on the left. When you get to that second one, you immediately go back to the first sign and carry on from there.
In the above situation, the repeat signs indicate that the passage is sung 3 times. The 1st time, just before you get to the 2nd repeat sign, you encounter FA LA LA where there is a notation of "1,2" above the bar lines, which indicates that the 1st and 2nd time you get to this spot you sing FA LA LA. After you sing the FA LA LA for a 2nd time, you go back to the 1st repeat sign once more. Since this will now be the 3rd time you've sung the part, when you reach the part just before FA LA LA, you jump to the part where there's a "3" above the bar lines and sing DUM DEE DUM.
Note that repeat signs can and do happen anywhere within a piece of music.
I hope this is all completely clear. I suggest that now would be a good time to entertain any questions you may have.
