Da capo is Italian for "from the head" or "from the beginning." You may have sung or played pieces that had this instruction, where you had to go back to the beginning and repeat part of the music.
In musical directions, da capo is often abbreviated D.C., and it's usually followed by al coda or al fine. If the sheet music is marked D.C. al coda, it means to repeat from the beginning until you reach another notation that says To Coda, at which point you skip to where there's a coda sign. The coda sign looks like an O with a plus sign through it. If the music says D.C. al fine, go back to the beginning, and repeat the music until where it's marked Fine, "the end."