What is Darknet?
DarkNet is a framework used to train neural networks; it is open source and written in C/CUDA and serves as the basis for YOLO.
Darknet is also used as the framework for training YOLO, meaning it sets the architecture of the network.
Clone the repo locally, and you have it. To compile it, run a make. But first, if you intend to use the GPU capability, you need to edit the Makefile in the first two lines, where you tell it to compile for GPU usage with CUDA drivers.