Ok so this might seem like a stupid question but still. So I just read online instructions on reading sheet music. I understand that the spaces are FACE and the lines are EGBDF, what i want to know is that when the note is shown to be either in between the lines or on them, which octave do I presume the sheet is for? Like if the note is shown to be an E is it an E4 on the guitar or an E5? or if its on the bass cleft it is supposed to be an E0 or an E1 on a piano? Please help I'm really confused.

The E in FACE is the highest string of the guitar played open. The E in EGBDF is the E on the second fret of the guitar's D string.

Guitar music sounds an octave lower than it is written. Middle C is 1st fret on the B string, which is written 4th space up.

No, guitar music is written an octave higher than concert pitch. All pitch is relative, and concert notation is no more privileged than guitar notation. If I understand the question, it's asking about the guitar, not about concert notation.