Explore a loaded model
Once you have a model from PyTorch Hub loaded, you can use the following workflow to find out the available methods that are supported as well as understand better what arguments are requires to run it.
dir(model) to see all available methods of the model. Let's take a look at bertForMaskedLM's available methods.
>>> dir(model)
>>>
['forward'
...
'to'
'state_dict',
]

help(model.forward) provides a view into what arguments are required to make your loaded model run
>>> help(model.forward)
>>>
Help on method forward in module pytorch_pretrained_bert.modeling:
forward(input_ids, token_type_ids=None, attention_mask=None, masked_lm_labels=None)
...

Have a closer look at the BERT and DeepLabV3 pages, where you can see how these models can be used once loaded.
Other ways to explore