Basic steps to develope a website

[eluser]kanjimaster[/eluser]
It sounds as though you may be confusing a framework (i.e. Codeigniter) with an application (such as WordPress). An application will have most or all of the features that you asked about already built in. A framework generally won't and is used to build them.

Unless you have a good reason to want to build these features yourself, you might be better off starting with one of the open source Content Manager Systems pre-built for you using Codeigniter. For example PyroCMS.

[eluser]AM-Info[/eluser]
Just visit that site ellislab.com/codeigniter/user-guide/ you will find all answer of your query.
Codeigniter Developers