How I can create users in Subversion.
For when people access the repository, only to see their projects or files and not those of the other people?
Answer depends on how Subversion server is setup.
If you're using httpd then it depends on how authentication is setup in httpd. See SVNBook | Authentication options.
If you're using svnserve then you can use the built in authentication setup.
And if you're using svn+ssh:// then either users log into ssh as their own user (in which case how to add users is a function of adding users to ssh) or they log into as a shared user and the --tunnel-user argument gets set.