I suspect that if you had the authority (and the responsibility) to do this then you would know how to do it. Or one of your coworkers would.
You say you are “the user.” Did you create the instance? If not, go talk to the one who did.
Generally, “users” do not create other accounts within an RDBMS. that is the job of the DBA and possibly the SECURITY staff. In cases where users actually create other users accounts, generally there is a program in place to accomplish this task. Users don’t generally issue this sort of statement directly.
On the chance that you are not trying to circumvent anything, but are at home trying to learn to use Oracle: the answer is CREATE USER statement.