Workflows and best practices for pull requests?

[Kevin Horton]

I'm new to working with a team of committers, and I'm a very basic git user, so I'm struggling to figure out workflows and best practices when making a pull request and reviewing comments on a pull request.

Questions:
1. One of the checkboxes when making a pull request is "squashed and minimized your commits".  I tend to make many small commits when working on my personal projects.  What is the best way to squash those commits before making the pull request?  Google seems to suggest an interactive rebase is the way to go.  Comments?

2. I'm completely baffled by the GitHub interface for dealing with comments on a pull request.  Assuming I have made and testing the changes suggested by reviewers, what is my next action?  Make a new pull request?  Is there a way to modify the existing pull request?  

Thanks,

Kevin