If you are not used to learning an instrument, here is a suggestion.
I would start out very simply by learning two chords and getting your fingers moving between one formation and the next, then back. For example, in the Johnson book, exercise 1, you could practice F7 to Bb7 to F7 to Bb7 …
I would practice this until you are fluent, then in iReal Pro you can either make a song exercise just for this or find the two chords in a song and loop them. Start with a very slow tempo enough so you can get the finger formation correctly each time the chord changes. (Your fingers need to be on the neck in position before you strum the new chord and you need to practice being accurate.)
Movable chords (meaning no open strings are used) mean once your fingers can automatically make the formation of shapes moving from chord to chord fluently (coming with practice from slow to a little faster over days or weeks of regular practice) you will be practicing the same thing no matter what the letter name the chord is (or key you are in) so it will work in all 12 keys.
Once you can do this, simply moving your hand up a couple of frets gives you G7 to C7. Practice mode in iReal Pro can be set to change the key on each chorus (repeat) so when you are fluent, you can practice moving your hand up (or down) with each key change depending on your settings.
Another simple chord change (very useful in jazz) is the II-V progression … Dm7 to G7 for instance. Exercise 3 the first couple of measures shows you this. Again, do not attempt the complete song, just get this change fluent. (I would try one chord per measure or even change every two—not both in the same measure to begin with.)
You can quickly sketch out the two diagrams on a piece of paper for reference, but after a while your fingers will learn the feel of finger movement from one to the other and by only having the two, you should be able to quickly learn it in your mind.
I hope something here is of help.
No unfortunately, you cannot add your own diagrams within iReal Pro.
