I'm a keyboard player. Maybe, this will help. C7 & CMaj7 have one unique difference. The Maj7th is one fret higher on the guitar. That's it. So, to go back to the keyboard it's one half step higher. The four notes within the chord would be
C E G B. Many ways to play but that's the root. When you see C7 just remember it's one fret down B- for guitar C E G B- Hope this helps.