E Commernce Site Building

[eluser]Sarwar CSE[/eluser]
Hi,
I want to develop a professional e-commerce website in codeIgniter. So i need some answer some question. The question is given under below.

What feature an ecommerce web site should have?
How I develop those feature in codeIgniter
When I ensure that the our site is fully secure
How should I plan an ecommerce site

I am new in ecommerce site building. please help me how can i develop a full successfully ecommerce site and what should an ecommerce site satisfied?

please help me.....