"Time Machine" I'm confused.

I just reformatted my external HD to use TM but I'm not sure of one thing.
Others use this computer (family members) each has an account on here.
When I set up TM to save, will it save the others accounts?Or does each account need to set it?I sure hope I only have to or the memory is going to get eaten up awfully fast. Anyone out here know?

Time Machine backs up everything on the HD (unless you tell it to exclude things); including other accounts files'.

As to whether it will run while logged into another account, or just record the changes and backup when logged into the admin account I don't know, but I suspect it's the former.

it would make more sense that it simply backs up your entire drive except for the parts you tell it to not backup. the entire drive would encompas all your user acounts