Efficient net as backbone network in few shot learning

I am new to PyTorch, so not sure how to use efficientNet as backbone CNN model for feature extraction, so that embeddings of images can be generated. As most of example on GitHub use 4 layer ConvNet so I can not understand how to use same thing for large CNN model. Like there are implementation of efficient-net for Torch, so what steps I need to use them as feature extractor?
I am using this efficient net code which implemeted network in PyTorch -