You should try to work from sheet music as much as possible. Nearly all sheet music is arranged for piano and this presents problems for guitarists. Piano music uses three staves thus:
A guitarist need only look at the top stave which contains the melody line (the tune), lyrics and the chords. Sheet music does not indicate what rhythm the guitarist should use. This is where your creativity and background rhythm playing must be put to use. See Progressive Rhythm Guitar by Gary Turner and Brenton White.