Thank you so much , I have 1 more question. Why did you keep saying don't forget diminished seventh chord. What should I do with it ? Just play all diminished seventh chords in the scales I practice ?
Yeah, I guess I was a bit strident about that.
Think about the diminished chords (or perhaps even the octotonic diminished scale, maybe for a future time) as giving you the maximum tension.
A lot of the altered dominant sevenths are borrowing bits from diminished harmony. You don't have to hit the theory right now, but you'll want to get that sound in your head and under your fingers, I'd bet.
And I'd bet you anything that you already know the sounds, just from being a fan of music. I presume!
It's just a particular chord that is the very definition of an unstable structure that can't help but want to resolve to the tonic, the tensions, that is. Or resolve to another key center.
I'd call it kind of a skeleton key for introducing motion into your chord progressions.
A plain dominant seventh chord is the same way, just often not quite as extreme. Or the IV6 chord, for that matter.
It's one way of thinking about the essence of what makes a cadence compelling, what makes it sound "right" or inevitable.
Plus, they just sound cool!

I'll
edit to toss in something that may not be in your wheelhouse yet, but let's say you want to play, say, a major scale, and you want to harmonize it. A legitimate way to do that would be to introduce diminished passing chords as you're preparing to hit, say, the subdominant triad or whatever. Very legitimate sound, you've probably heard it at least in the background as what are sometimes called just "block chords" in jazz or pop piano (George Shearing, Bud Powell, you name it, it's just a standard way of introducing an inevitable motion into what, to me, would just be an utterly boring series of triads which would lack most of the tensions that make chords make sense.
I suppose you could say tensions, or maybe just the one tension of the leading tone makes chords come alive. Otherwise it doesn't have too much flavor.
Now, yes, there are a lot of exceptions, and some very good music came out of subverting the traditional common practice period harmony. But those are more "yeah I'm consciously going to break the expectations and do something different." So, two well known examples from jazz come to mind: Sonny Clark's tune and playing on "Melody For C," or....well I was going to also add Bill Evan's tune "Peace Piece," but he wasn't using triadic harmony, not really. The Sonny Clark tune, though, IIRC is built off i think what you're trying. More or less just diatonic triads (well, extended to the degree of the seventh, major or minor) to a melody which is just a fragment of the C major scale, as you might have guessed. It's a very plain, unsatisfying sound, which is what makes it sort of exciting: how are they going to get some music out of that nothingburger of a tune? It's up to you if you think they succeeded or not.
You'll also note on "Melody for C" how much tensions derived from the diminished scale or chord Sonny Clark uses when he employs the authentic cadence in his improvisation. He even outlines the diminished seventh chord tones at least once, so you can tell where his head was at, just as Bach was all about that too.
Just hit the authentic and plagal cadences in all keys, and then if you do have a theoretical bent, you can work on Neopolitan harmony and other exotic sounding things like other augmented sixth voicings, and do more work on minor harmonies, and fool around with "double diminished" voicings and all that.
I'd really stick with the basics, though, at least for now: it'll sound good, you'll use those cadences the rest of your musical life, every single day. Nobody ever got fired for playing a nice set of chords, I think is how the old adage goes.