The BIA is the hub for documenting how your organization produces its final product as well as what resources support the creation of that product.
First, a BIA should be created for each department/ business unit in your organization. Each BIA records the activities/processes performed by that department. See the article Maximizing your BIA: Linking Products/Services to Activities if you have not already linked your Products and Services to your BIA.
You will want to add all of your necessary Department/business unit's activities/ processes to the BIA if you have not already done so. Once the activities are created you can then move onto connecting your dependencies.
Application, Facility, Supplier, Department, and Other Dependencies will all allow you to link the items to an activity through Activities using this [type of dependency] Dependency field through their respective create/edit forms. The field is a checkbox field that just requires a check mark placed next to all applicable activities that the dependency supports.