The question may sound kind of funny at first, but when you think about it, it's a valid question. Like buying a pair of shoes, the use they will be put to determines the type of shoe you buy. Otherwise, you'd look pretty silly on the tennis court in wing tips. So, what do you want your website to do? What message do you want to send? Do you want to sell stuff? Save the world? Dominate the world? The clearer you can define these questions the better your website will fit you and your purposes.
The answers to this basic question provides a lot of information about what you will need for your website. For example; if you are going to sell products online, then in addition to the shopping cart (ecommerce) package, you will need a merchant account, to allow you to accept credit cards (unless you already have one) a Security SSL Certificate and a dedicated IP address because your new Certificate won't work without one.
EXCEPT: when you don't need any of that! There are literally tens of thousands of people happily selling products and accepting credit cards on the web who have no Certificate, dedicated IP or merchant account. It's quick, easy and the thing to do under the right circumstances! This is why it is important that you have a website developer who will take the time to ask these questions and discuss your options, and their ramifications, with you.