Play Adim7 one string at a time and you hear A, C, Eb and Gb. A is the root, C the minor third, Eb the flat fifth and Gb the diminished seventh. Said aloud, its notes are A, C, E flat and G flat. Each note sits three semitones above the one before. Slide the same shape three frets and you get the same notes.
String by string, low to high, it plays A, Eb, A, C and Gb. Of the five strings you play, two give A, the note that names the chord. It runs from A on string 5 up to Gb on string 1.
In Adim7, only one string rings open, string 5, which gives A. Avoid string 6. Your hand covers two frets, from 1 to 2. This page has three positions. The others start at frets 4 and 7.
Change only string 4 in Adim7 and you have Am6. Adim7 and F have A and C in common. Bm shares one position with this shape.