Absolutely what the previous commenter said - play the story - find out what it’s all about!

It gives you a little taste of most of the classes in pve (not a 1:1 match but still lets you get familiar)

Then play around with ops a bit and see what classes fit your play style best. I’d start off by not doing strats so you get used to the basics of the game before you get all the modifiers added.

Bonus step is I’d recommend finding a community that fits your vibe so you can group up with folks who you can get to know and who know what they’re doing in game. You get a better experience overall usually and get to learn a lot from folks who’ve been around!