You can add and remove Modules depending on your website package that you purchased.

To add a module go to YourDomain.com > Module List

See Screenshot:

Once on this scren click on the green "add Module" button.

you will be taken to a screen that looks like this:

On this screen you can choose from the drop down list what Module you wish to add.  This list is limited by the website package you purchased. 

If you wish to purchase a module that isn't showing in your drop down list you can purchase add on Modules for existing clients here.  Or feel free to contact support