how you people manage when you join a new team where work is completely new from your previous te experience.

I take my time to learn it 🙂

but tasks wont wait for so long

It doesn't have to be so long. You don't need to learn the whole codebase or all the new projects. Just the essentials around the task assigned to you. Communicating the same with your manager will keep their expectations in check for the initial phase. They should understand this as you'd not be the first new person in the team (or maybe you are 🙂 ).