Templates can depend upon other templates, which will be installed alongside them. Separating templates into smaller applications which install eachother helps avoid data duplication. For example, if you already have a Contacts template installed, the Customer Relationships or Sales Leads templates can use your existing contacts instead of adding their own.
If you have multiple installed versions of a dependency, you can click the dependency's name to see a page listing its installed forms, and confirm the correct version to install.