In Privileges, It says creating posts is a privilege limited with 1 reputation. Then If someone's reputation drops to 0, can't they create posts?
Reputation can't drop to zero. It never falls below 1.
\$\begingroup\$ Woah. I did not see that. \$\endgroup\$– user54200Jul 7, 2016 at 12:41
\$\begingroup\$ @MatthewRoh well, it's not trivial indeed. \$\endgroup\$– user8790Jul 7, 2016 at 12:51
Creating a post is a privilege, because it can be taken from you. If you post too many badly scored questions or you delete them there's a chance you won't be able to post any more.
Because reputation can't below 1 (as others noted) this is the only way to lose this privilege.
3\$\begingroup\$ Not really relevant. Question or answer ban isn't related to reputation directly, i.e. user with 1000 reputation can, in theory, be question banned. Suspension on the other hand, is the one thing that blocks all privileges, including posting. \$\endgroup\$– user8790Jul 7, 2016 at 12:52