Unity Building Blocks are a starting point to quickly add functional features to your project. Each Building Block contains assets and scripts that give you an example of how a series of features work to achieve an outcome. You can download Building Blocks from the Asset Store.
You can add a Building Block to your project at any stage of development. Each Building Block contains a test scene that you can open to test its features.
Building Blocks exist on the Asset Store. To learn how to add an Asset Store package to your project, refer to Purchase or download a package from the Asset Store.