A bit more info would help, namely what experience you already have and what character(s) you're planning on using.
Most find it best to hit up the in-game tutorial, action/combo dojo, and single player mode (to unlock everything) when starting out. But I can see most people wanting to skip that and get straight into PvP/online matches.
Coming from Smash isn't all that different in terms of what basic fundamentals you're gonna need to learn. You need to memorize what beats what (the Attack Triangle, as well as when to shield/jump/back away, etc.), learn what special attributes your character(s) have, and how to cancel moves/find what can be strung together (cancelling usually involves specific button presses, either with a different attack or the shield button). Just like any other game, you should be able to find both basic and advanced guides on just about any medium (Youtube, Reddit, the character forums here, etc.).
The rest of it is pretty much just persistently practicing and playing people. Combos eventually start feeling natural once you get comfy with all of your moves, and getting good going hand and hand with learning things like match-ups/neutral. It takes time, but it's worth it.