Sharps # and flats b
These symbols change the pitch of a note. A sharp sign (#) takes the note a semitone higher, one fret higher.
If I want to find a C# (C sharp) I just find the normal C and move it up one fret to get the C#.
If I want to find Bb (B flat) I just find the B and move it down one fret to the Bb.
So, to sharpen a note, you take it up one fret (up a semitone). To flatten a note, you take it down one fret (down a semitone).
Pitch refers to how high or low a note is. If you move a note on a string towards the body of the guitar then you are going up in pitch. The highest pitched string is the 1st string (nearest your leg or floor), the lowest pitched is the 6th string.