how to start these quests?

I don't know how to play any of these

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/72 and /50 isn't even worth the time to do.

/10 is instance, you can auto queue for it, but very few people do it. You will likely not ever get 6 people doing it at once to succeed with auto queue. If you got some friends, you can bring 1 or 2 people and manually enter. Manual entry is 2 people minimum.

11:30-12:00 is guild activity. My guild does it at 7:30pm server time.

Last one is guild loot box. Doing instances gets you gold nugget drops. 10 of them can be traded for a key from an NPC in your guild base. He's to the right of where you spawn when you go to your base. Then you have to look for red/yellow pouch on the ground in your guild base and use the key to open them.

That thing between /72 and /50 I have no idea.

I mean, any of ALL the quest from that window, the bosses, etc