Hello, for now I will telling you of about 'Different of 7 and +7 Chord. Okay, I will explaining first, what it is 7 is type?. 7 or we can say 'Dominant' is plus note function, example if we use C key then we add some '7' = C7, so note color will be heared like dominant on other focus key (not on C note again). Here is the simple image.
at the up you can see that is C7. Like I said before, note focus was changed and changed to Bb.
And what it is '+7' ?. We can say that 'Plus Dominant'. '+7' just have 2 chords, and did not having other paralel of notes. Notes of +7 just having notes it is of self. Notice this image.
You see that?, did not have others paralel of notes, and Dominant chord still C (not changed). Okay, that is all for simple learning. Then See you next time in new learning...