In order to enable the Familiarity feature, you will need to sign at least 1 contract in the Deal type. To get the best possible experience from this feature, sign as many contracts as you can in each deal type.
Signing one contract in a Deal type will enable the feature, but you will not see its full functionality. To enable the part of the feature that compares the contract against a 'template' or 'standard' document, you must set at least one template contract for the deal type.
Our article on Enabling Familiarity provides more detailed information.