So how does the damage work as the snake if i constrict. i roll to hit / save. it hits and they fail the save. when do they take damage, on my turn do i roll constrict again and thats it? can i bite also? This is my firs time playing DnD and my DM is not clear on it either.

You can either bite or constrict.  If you have a creature constricted, they are considered Restrained so you will have advantage on your attack rolls.  Even if you have a creature constricted, you still need to make the attack roll.

Ok, so I don't roll the constrict as damage on my turn with a hit as well as biting as my action then. The constrict hit would be my action?

Yes, you would use your action to attempt to hit them with constrict again.