I haven't been playing long. Anyways in sheet music, what do you do or play when there is a semi horizantal/diaganol line through the note? Thanks

It depends on what the note is. For example a quarter note with one line through it would be played as two eighth notes, two lines would be played as four sixteenth notes, etc. It's a sort of rythmic shorthand used in notation when the part calls for repeated notes. One printed measure of four quarter notes with two slashes each, for example, saves space and is an awful lot easier on the eye than sixteen sixteenth notes.

David K:

He might be talking about appogiatura or grace note. Diaganol line through the note? I don't know. What do you think?

Well, the line is only on half, and quarter notes I think. And the line is diaganol. I don't know why it would mean play it as two quarters, or eighths, because in some parts, there will be a couple eigths and then a quarter note with the line in it. At first I thought it was for vibrato, but it was on a couple open string noters.

A diagonal line through the stem of the note indicates exactly what I described.

I guess you're right. It just seems odd.