Notes that are raised by half a step (one semitone) are considered "sharp".
Indicate a sharp note by placing a ^ (shift-6) before the
note name.
play "F ^F G F"
Once a note is indicated as sharp, that note will continue to be played sharp until the end of the measure or line.
Indicate a natural (unsharp) note by using =
before the note name:
play "^C G C =C G C B,"
Occassionally a double-sharp is needed, and it can be written as ^^.
Read about key signatures if you are writing music with many sharps.