How does seating work?

Right now I have middle seats, is there a chance that an aisle/window would open up or do you have to pay for those? Should I just keep randomly checking, or is there a strategy?

I see there is no iphone app for Virgin America.

So I assume you have to checkin old school at the gate or online?

This will be my first time flying Virgin America and I am very excited about it, thank you all so much for your advice.