More than just understanding basic combos from c. B/low jump attacks, it's also important to understand your characters' basic mixup options so that you have ways to open your opponent up (or with a zoning character, keep them at a manageable range).
Even if you're not always landing optimal combos, if you understand how to limit the opponent's options with your character, you can kill the opponent with repeated small victories instead of one or two decisive blows. Learn how to create traps for your opponent's common reactions (roll? DP? CD counter? keep blocking? mash from disadvantage? jump predictively or on reaction?), and exploit those with simple but consistent punishes to keep your momentum. (You bait your opponent's roll out of your corner pressure, but you don't know/can't do any good combo punishes for it? Then you can at least throw them back into the corner and try to counter whatever they try next to escape. Any punish beats NO punish, any day of the week.)
This game scares a lot of people due to the high-end execution requirements, but many new players don't realize how easy and rewarding it is to create a fundamental game to build on. If your combos are still developing, there are plenty of universal offensive and defensive tools to fill out your basic mixup and zoning. Worry first about learning how to poke, zone, move and mix up at the basic level, and grow into bigger and better combos as you get better at creating opportunities for them.