The same note at the exact same pitch can be found 5 frets lower on the string physically below. For example the A note at the 5th fret of String 6(E) is the exact same pitch as the open String 5(A).

To find the same note on the string physically above, you simply do the opposite, moving 5 frets higher. For example the C note at the 3rd fret of String 5(A) will be at the 8th fret of String 6(E).

Explore this idea on the different string pairs and make sure you get that 5 fret forward/back connection clear in your mind.

[We'll see later how the unison is 4 frets forward/back between Strings 3(G) and 2(B)].