Hello and welcome to the community Stephen.
That is the fundamental, the instrument we play is, at heart, a rhythm instrument (with some added bells and whistles like notes, chords etc.).
100% true.
Ah, but you had a capo at fret 2 so the chord you’re playing in the pic is an E major, not a D major! 
Richard
Richard,
You are absolutely correct. After 40 years, you would think that I would remember that the capo changes the key. I was a little sloppy in the language and meant to say that since I was playing a chord shape of the D chord, that I was probably using the chord forms, shapes or grips of the chords from the keys of G, D or A, which means I could have been playing in the keys of A, E or B.
To be clear, I mean the chord shapes of the major open chords of the keys of G, D and A or the I, iV and V chord shapes of those keys (key of G - G, C, D, key of D - D, G, A and key of A - A, D, E) which all have a D chord. I’ve had just enough exposure to music theory to learn about the harmonized scales, the amazing circle of fifths and some other basics. I encourage anyone who hasn’t had any exposure to music theory to look at Justin’s practical music theory course. With a little music theory you can reduce the memorization of chords and make the guitar fretboard seem more logical.
Welcome! I hope you have a fun time playing and get good use out of all the lessons! 
Thanks!
HI Steve,
It is amazing that you have been playing guitar as long as I have been living and although there were challenges along the way, you never gave up. Your story is inspirational to me and makes me realize the power of never giving up on your dreams of playing guitar. I started playing around 2004 and was pretty awful at it, no formal lessons and just muddled my way through learning chords through random DVDs and books. I sounded completely awful. About 2 years ago I stumbled upon Justin’s lessons and have taken leaps and bounds in progress through his methods. They really work well and now I play in front of people with appreciation from the crowd instead of people running for cover. Keep up the progress and good luck.
Jeff from California.
Thanks. It sounds like you are benefiting a lot from this site. I look forward to future progress and playing in front of others.