The crowdfund extension is a premium plugin that only works with the pro version of NM Gift Registry at the moment. There are plans to make it work with the lite version later. However the features would understandably be limited to the capacity of the lite version.
To install the crowdfunding extension, you need to have the pro version of NM Gift Registry and Wishlist installed first. Then download, install and activate the crowdfunding extension like any normal plugin. You can start using its features straight away.