E-Commerce and Shopping Carts

How do you go about building a ecommerce or shopping cart for my business. What software is the best for shopping carts. How does it work. What do I have to ask my hosting provider or what kind of hosting do I need. How does verisign or etc. works and what is the best to use (versigin,etc….. I need help, so I go in the right direction. I don’t want to make any costly mistakes.