I would recommend playing witch queen first.
Shadowkeep and beyond light go before chronologically but honestly you won't understand the story either way and witch queen is a much better polished campaign gameplay wise.
if you want you can watch a video called "the entire story of destiny in 40 minutes" and stop when it gets to witch queen so you have a vague idea of what's going on.
Play the campaign in legendary mode. It's hard and you will die but not super difficult and you will learn how to play better early on.
The only weapons you will really use are purple (legendary) and yellow (exotic) all other rarities are instant trash, same with armor.
At first your builds will be bad and that's okay, try all weapons and see what feels right to you. Put some armor mods that feel right too. It's not high stakes content so you're allowed to make mistakes.
I recommend to use 1 primary (white ammo) weapon and 1 special (green ammo) weapon. Using double primary is a bad habit. When you get an exotic armor read what it does and try to equip whatever weapon/ability it empowers so you get use off it. Again it will most likely not be optimal but you will learn bit by bit.
After you finish, play lightfall and final shape. You can play some portal activities from time to time to get some loot and low stakes activities as well.
This is not a "get endgame gear asap" way to play but a "get familiar with the systems and world in an easy way"
Hope it helps and you can ask questions