This is just an example for a mod that can interact with Vampirism's API if Vampirism is installed. It also runs without Vampirism and adds a "super cow entity" which can be converted if Vampirism is installed.
This example mod does not require Vampirism to be installed. Check out the other examples for a addon style mod example.
Vampirism's API is declared as optional dependency in the build.gradle file. Adjust it to use the latest version. It will be downloaded automatically when setting up your workspace.
Same as the MDK or most other mods. You can check out the guide in the Vampirism repository.