They are two completely different concepts.
If I jump/crossup/whatever you, and you do a DP, Flash Kick, or whatever, it will autocorrect. I don’t know the exact timing, but this will explain when you DP as the opponent goes over you. IIRC, not every special has this trait.
Option Selects involve you performing overlapping inputs. Depending on the situation, the game will choose the best option for you. Here are two examples:
Crouch Tech - You down back and do LP+LK. If you do this away from the opponent, you’ll get a cr.LK. If you do this as your opponent tries to grab you, you’ll tech.
Canceling into specials - Let’s say I do cr.MK with Ryu. When I do that, I do the input for canceling into the Hadouken. If cr.MK connects, I cancel into Hadouken. If cr.MK whiffs, the Hadouken doesn’t come out.
You can find tutorials for beginners on Youtube. If you’re lucky, you’ll find character specific tutorials.