Using PGAdminIII create a database using the template_postgis as a template, this copies all the triggers, functions and tables into a new database. Right click on the databases symbol and select 'new database':

Then you can import data into it. It is probably best to not use the pg_admin user but if you're the only one seeing the database that should be fine. Have a read of Roles and Privileges to see about creating a 'user' or users identity(s).
If you don't have template_postgis in your database then perhaps you can create it (or here) but I found it best (easier) to uninstall and reinstall PostGIS.
here are the screenshots in sequential order.
– Christopher Harrod Mar 11 '15 at 04:50