Above (and below!) are the main notes over the first 9 frets of the guitar.
So the note at fret 5 string 'g' is a 'c'
The note at fret 8 string 'a' is an 'f'

Notice that 'b' and 'c' are always just one fret apart everywhere on the fretboard.
The same applies to notes 'e' and 'f'

Where are the 'sharps' and 'flats'?
They are in between your main notes.
For example g sharp (g#) is always one fret  above any g on the fretboard.
So the 4th fret on string 'e' is g sharp (g#)

A flat  is always one fret below any "a" on the fretboard.
So the 4th fret on string 'e' is also "a" flat!

Find any d sharp (d#) or e flat  (eb) on the fretboard below...
Try any "a" sharp (a#) or b flat