#2
only mods can lock/close threads.

if you made a thread and you would like to delete it, click the edit button under the first post of the thread, and the option to delete is there.

if you think someone else's thread should be closed because it breaks the rules, click the report button under the first post of the thread (it's got an exclamation mark on it) and report the thread to a moderator.
from daylight...
...into darkness