Firslly, you can test your oracle  status by "lsnrctls
status" command on your command line or your terminal.
and also, if you have installed  the db server  on the
windows OS, you can test it in your control
panel/advanced tools/services. oracle_homeTNSListener
shows your db status.

For your second question, I must to tell you, you can
add oracle objects such as tables, sequences and etc.
in some different ways. The first one, you can add it
by Oracle Enterprise Manager, the 2nd one is dbconsole
it is an online Enterprize Manager and the 3rd one is
sqlplus(I recommended). you can type sqlplus in your
terminal and go to the sqlplus enviroment after typing
your username and password and create  everything you
want;-) but befor these, you have to create a db
instance via bdca(DataBase Configuration Assistant).

I think oracle.com can be very usefull for you.