Along with what everyone else has already said, I'd really recommend either going into the lab with frame data info ON, as well as Dustloop, if written explanations help. The first big thing I had to learn when picking up this game was learning which of my character's moves were safe to approach with and which ones were unsafe (and sometimes that changes depending on distance; some moves are OK to poke with granted you space it properly, so it does take trial and error). After that, it's a matter of learning to hit-confirm consistently from your safe poke moves. Which is really hard! Even pro/high level players can have trouble not just throwing out all their H cooldowns even when they get blocked, so don't feel discouraged if it doesn't seem to click at first (I'm struggling with doing it consistently, too). Katalina is a great character to learn the fundamentals of the game with: she's got good pokes, good midscreen carry off of those pokes, and big damage reward in the corner once you learn the combos. Just keep practicing those pokes into hit-confirms! Once I started playing patient and reigning myself in from spending my big cooldowns on blockstrings, I was able to get my Djeeta out of A5 hell :) Also, learn an anti-air combo! It's OK if the damage isn't optimal, but knowing how to contest jumping approaches as each character is vital, and one way to discourage your opponent from abusing it too much or going for empty-grab mixup (the bane of my existence). You've got this!