sharp sign. flats look like little (b)s, like this, ♭, naturals look like a a rectangle with one line coming out of the top and one from the bottom, ♮, and ledger lines are a short line added for notes above or below the range of a staff. basically, lines where there is supposed to be a staff's line, but it's on the blank space on top or on the bottom, to show you there is supposed to be one there. (see picture attached)