If you want to learn the positioning of all the 5th chords then learn the notes on the thick E, A and D strings. As discussed in "5th Chord Shapes", root 6 and 5 are the two most common 5th chords. So to make it a little easier for now, you can just learn the notes on the E and A strings. If you learnt the "Bar chords" section you should all ready know these notes.
Playing this root 6 position 5th chord from the 1st fret would would make it an F5 chord. I f you were to play it from the 7th fret it would then become a B5 chord.
2 String 5th Chords
3 String 5th Chords
What ever note the 1st finger is pressing down on the 6th string is the name of the chord. This note is called the root note.
The diagram below is showing you where you could play three different B5 chords on the fretboard. The first two (root 6 and root 5) will sound the same, but the third (root 4) will sound higher (1 octave higher). The same rule applies with 5th chords as does with bar chords, if you have two chords that sound the same but are placed in two different positions on the fretboard then play the closest chord from where you are.