You better check with installation guide for setting up installation procedures. If your installation is perfect and it went well and your default database works fine. Everything is ready to go:

1.Prepare init.ora parms file
2.design physical layout/Follow OFA
SETUP environment ORACLE_HOME and ORACLE_SID
3.create database, create rollback tablespace and rollback segments, TEMP, USERS and TOOLS tablespace
4.run catalog.sql and catproc.sql
5.run other options scripts as needed like replication option, dbms utility scripts etc.
6.Create data and index tablespaces for Original database.
7. oratab eith the new instance created
8. update listener.ora,tnsnames.ora,sqlnet.ora
9.alter database backup controlfile to trace.
...
..
.

thats it pretty much