Go to netbenefits.fidelity.com, set up your log in. In there you can choose to open a 401k, Roth IRA, I think regular IRA is also an option. You can choose the percentage of each paycheck you want to go to any or all of the accounts (Starbucks matches 5% to a 401k). You can also set it to increase your contribution by 1% each calendar year if you want to be a little sneaky with your future self.

I find their user interface to be a little confusing, honestly, but the 401k part is pretty clear, at least from what I remember when I set it up.

(Also accept any bean stock grants you may have while you're there.)