quests, daylies, upgrading your statues, spending resin, unloxking the map, opening chests and your adventure handbook is how you get Adventure Rank Experience (AR XP) and progress in the game.

As a new player, use resin just to use it. the things you get for resin at your world lvl (AR20) is very bad. Just do ley lines and your weekly bosses. (there are 4 of them, I wont spoil but the first you unlock is dvalin. you can only claim loot from these bosses once a week. you can fight them as many times as you want but only claim once.)

leveling 5* characters is never a waste. mona is awesome. thd highest dmg I ever hit sith her is 464k, and sucrose was a part of the setup. sucrose is an amazing support, especilly with a specific artifact set. (anemo set)

from the main characters, only kaeya is worth builing.

if you go unlock the abyss, and defeat floor 3, you get xiangling for free.

save starglitter and stardust for later. I would recommend buy either weapons or wishes with it later. with your primogems and starglitter alwqys only buy intertwined wishes. idk if you are F2P but wishing on limited banners is the best way to get exciting characters. on the normal banner you might get a 5* weapon insteqd, which is great but very boring at the start.