You don’t know how to counter “beginner” tactics yet, such as repeated jump-ins and Shoryuken spam. “Better” players usually play more carefully, which means they won’t steamroll you and give you time to think and read them.
So to fix this:
Learn how to counter dumb moves like jump-ins by getting your anti-airs down pat.
Learn your basic punish combos to punish the gaping openings that are bound to present themselves.
Learn to play with the sole intent of punishing unsafe moves, while giving your opponent no openings of your own. Bad players will throw unsafe moves with reckless abandon, allowing you to decimate them in a few combos if you’re patient.
I’d start in practice mode. Record what’s been going on, try to recreate the situation. You sound like you’re mildly familiar with this stuff so you could do it. The dreaded practice word is usually a killer however I think if you just record some stupid jump ins with characters and practice dragon punches or what have you first, you’ll conquer half the online community.
After that, go looking for the threads concerning who you want to play, then watch some youtube videos of how its done and what it looks like.
Oh and if you’re not sure how to block, hold back. Crouching block is down and back together. Remember this though, its like rock paper scissors. Standing blocks overhead punches and aerials but you can go down from lower attacks. Crouching block guards upper and lower but not over head so be careful and remember that.
One thing I found useful was to record an tireless assault of punches and kicks and guard as much as I could till I got it down.