I have seen that some people can delete others' comments. Can only moderators do this or can anyone with a high enough reputation? Also, can my answers also be deleted by others?
Only the person who posted the comment and diamond moderators can delete other people's comments - 10K moderators can't delete comments (note the absence of any reference to comment deletion in the list of permissions on the various FAQs, e.g. Meta's FAQ).
Diamond moderators and the answer owner can delete an answer. Besides, users with 15 reputation can flag posts as offensive or spam. A post that attracts 6 spam/offensive votes will be automatically deleted (by the user Community ♦).
The SO faq states:
Other people can edit my stuff?!
Like Wikipedia, this site is collaboratively edited, and all edits are tracked. If you are not comfortable with the idea of your questions and answers being edited by other trusted users, this may not be the site for you.
As all content is posted under the cc-wiki license which is linked to at the foot of every page.