Learning the different seventh chords can be tricky.
Before you start out, make sure you know your major and minor triads, and the maj 7th (C-B), min 7th (C-Bb), and dim 7th (C-A) intervals.
I do love tables and graphs,so here’s one I made that may help you.
|Dominant Seventh||C7 (V7 of F)||C E G Bb||Major triad and a minor seventh|
|C E G B||Major Triad and a major seventh|
|Minor Seventh||Cm7||C Eb G Bb||Minor triad and a minor seventh|
|C Eb Gb Bb||Diminished Triad and a minor seventh|
|Diminished Seventh||Cdim7||C Eb Gb A||Diminished Triad and a Diminished seventh|