There's a "models" directory inside the directory where you installed the webui. This is where the model files should go, but they also have supporting files (.yaml or .json) with important metadata about the model.

The easiest way to install a model is to let the webui download the model itself:

And after it finishes downloading, just load it into memory by clicking the refresh button, selecting it, choosing llama.cpp and then load (perhaps tick the 'CPU' box, but llama.cpp can do mixed CPU/GPU inference, too, if I remember right).

My install is a few months old, I hope the UI hasn't changed to drastically in the meantime :)