Yeah, Smash experiance isn’t going to help you too much. Platform fighters like Smash are pretty different from traditional 2D fighters mechanically. For one thing, no Block button (shield button in smash). When you’re attacked you hold back to block. And if you’re standing or crouching when you block that determines your vulnerability (standing to block leaves you vulnerable to low attacks, crouch blocks leaves you vulnerable to high attacks) so you need to learn how to read your opposites moves.
My first advice… start with KoF XIII. Its newer and slightly more accessible. And what you learn there will be directly applicable to 2002UM (and most SNK fighters going forward). Next, use the Shoryuken KoF XIII Wiki page to read up on game mechanics, its pretty comprehensive all things considered. The Video Introduction and Systems 101 sections will be invaluable.
Next, get into training mode. Pick one character (anyone who looks coolest to you at the time) and just practice. KoF is a 4 button fighter, 2 punches, 2 kicks. Each button will do something different(normal moves), some will even do a different move if you hold a direction while pressing it (command normals). So push some buttons and hit a stationary target a bit.
Next you are going to need to learn special moves. These are completely different then anything you’ve ever used in Smash (unless you’ve played around with the recent Ryu DLC). Do a motion (like half circle forward) and press an attack button. Depending on your character a special move should happen. Each character has a unique move list (another big difference from Smash’s universal move inputs) you can find in the pause menu.
Then… just practice a lot. Read up on what you can, watch some videos of matches, either here or on sites like Dream Cancel. And then just stick with it. If you gel with it you’ll learn a lot that will help you in the future for playing every major fighting game you may try.