Aimeos is capable of handling multiple shops by one installation and each shop is called a "site" in Aimeos' terminology. The basic version of Aimeos provides you a single site called "Default" after installation which should be the base of your first shop. This shop instance will contain all products with all associated data you are going to set up, the configuration of the delivery and payment as well as the orders that will be created by your customers.
If you want to set up more shops, you are able to create an unlimited number of top-level shop instances which are independent from each other. The easiest way is to run the setup/update script and passing a new site code. This will create a new site with all required data including the necessary default data like the types.
Furthermore, the Aimeos company offers an extension which enables you to add sub-shops that inherit products, categories, pictures, texts, etc. from a parent sites. You can even add more sites to these sub-shops without any restrictions in depth. This is perfect for market places, reseller structures and complex B2B portals.
For switching between the different available sites, the administration interface contains a site selector in the upper left corner. The icon is only shown if there's more than one site you have access to with your user. Super users will see all sites, admin users only their own ones and editors can't switch between sites.
Depending on the selected site, you will see the data associated to this site. If the ai-sites extension of the Aimeos company is installed, data inherited from the parent sites is shown as well but can't be changed, only enriched.