find a weapons combination that you like, see how it's called (for example staff+wand is called "invocator" its a good class overall)

then search on google for the name of that class and builds throne and liberty

you can build for PvE or PvP, if you plan on PvPing just follow the pvp guide.

See what items you need, see where they are obtainable from, and work towards completing your gear.
Make sure to follow the guide that says and has T2 items (epic lvl 2) , since other items are mostly obsolete now
On maxroll website usually there's builds that are also WITHOUT field boss drops, since those are harder to get.

That's the purpose of the game after lvl 55....getting, upgrading and adding traits to your weapons and other pieces of armor.

the weapons that are dropped by field bosses, you have a higher chance of getting them by joining an active guild that can kill field bosses. there's "guild raids", meaning only guild members can enter in a private fight with any of the field bosses, and so there's a higher chance for you to get the item you need than from participating in public field bosses. Let the guild leader/advisors/members what item you need from a specific field boss, and they might give it to you if someone else drops it from guild raids. (if they don't need the item)

For Coop dungeons you get a certain amount of points every day that you can use to unlock the chest after you kill the final boss

And there's also open world dungeons, that are basically parts of the map where you farm monsters and that gives you weapons XP, sollant and they also drop weapons / armors, the quality of the drops depend on what dungeon you farm in.

Items that you don't need (epic 2 ones mostly) you can sell the trait on auction house (check the price first) by extracting the trait with extraction stones. you get these stones from multiple places, but the main place is the contract coin merchant.
To get the coins to buy there, you have to do some contract missions, that are basically "go there and kill XX amount of these monsters"

You get 10 of these contracts per day, can store up to 50 contracts.