Every single day you will be able to do various in game dungeons which will let you claim quite a lot of rewards, depending on which ones you are doing. I suggest that you do all of them, but if you don't have the time for it, let me tell you some of the best ones:

Abyss Dungeon: this is the EXP dungeon, and it will give you tons and tons of EXP and help you level up pretty fast early on, so it's a super good EXP source. It won't give you anything else, just EXP.

Guardian Angel Dungeon: it's a good dungeon, which will give you buddy boost items and some EXP, and depending on your level, you can choose the difficulty of the dungeon.

Glyph Tower: this is a super good dungeon if you are looking to get stronger and farm it quite a bit, because it will give you glyphs which you can inlay as you unlock the slots. This gets increasingly stronger, so you will need to make several upgrades before you challenge it again if you can't advance any further.

Team Dungeon: will let you team up with more players and challenge a stronger boss which will drop gears. It's good,but if you are looking to do just a quick run of dungeons, you can skip it because you can just challenge the world boss for gear.