Writing music is a very challenging and rewarding experience. However, there are certain basics that one must have before attempting to do so, no matter what type of music is being written. All music writers must be informed about clef, key signature, key, accidentals, etc. Clef is the first thing that one needs to know. If it looks kind of like an S, it s treble clef.
Tenor clef is bass clef which has been transcribed up five notes, and is much less common.
This tells how many sharps or flats the piece has. No key signature can have sharps and flats. These sharps and flats are added in a particular order, by fifths. These sharps come in fifths, starting with the lowest and ascending. With no sharps, the key is C major.