You have actually already worked a little with Lookup fields before—without even knowing it.
The “Contact” field in a Deal record is a lookup field. It “looks up” to a record within the Contacts module. These special kinds of fields create connections between modules and begin to form a really cool relational database.
In our business use case, we will create a lookup field in the Deals module called Affiliate, so that we can see which affiliates are referring business to us.