alias py='python'
Do I put that in my .bashrc?
Yes if you want to work for your use only then yes .bashrc is the right file. If you want it to work globally add it in /etc/bash.bashrc
If you have a lot of aliases it can be a good idea to have a special file for them (like ~/.bash.aliases) and source that in your ~/.bashrc
Yes. Don't forget to reopen your session. :-)