How to allow other users create databases ?

I have recently sucsessfully installed PostgreSQL onto my Linux system.
 I installed it under the user name of 'postgres' and able to create
databases Ok.

But when logged in as my normall user account 'pmoscatt' then try to
create/manage databases I get an error message indicating that I don't
have the permission to do so and that I am not in the catalogue of users
to do so.

How can I fix this ?

Pete