How to do a graph in Python? (and proper terminology)

[jpy]

Hi everyone - I have a few questions I hope you can help me with.

1. I am using Pandas and NumPy, are these called libraries?
   Is there somewhere I can see a list of all functions with what they do? I am focusing on using Excel within Python.
   
   

I also ran the code below:

pd.value_counts(excl['Pop']).plot.bar()

This code works but the graph is the same all across when it shouldn't. I would like to sum all values found in the 'Pop' column and group by the 'State' column.