This is simply the size of the tensor you are creating. In your case you’ll get a Gaussian distributed (64, 100, 1, 1) tensor.
This is again the size you are creating. In this case (as torch convention) the batch size is the first dim, and in torch.full you are creating a tensor of size batch_size filled with the required value.
Since both this methods can receive any size tensor to create (python *args), you can pass the size of each dim separated by commas.