Go to the parking permit office it is in the main terminal prior to security on the upper level, bring your DEN SIDA badge. If you do not have a DEN SIDA badge you need a letter from someone important in your company on company letterhead from a company that works at Denver. When at the parking office you can get a parking permit for the employee lot (airside or landside.) You need a SIDA for airside. If your company doesn't pay directly then you'll have to pay there.
If you're getting your DEN SIDA badge make sure you tell them you'll park airside as there is an extra step they have to do at the badging office otherwise you wont be able to get through the turnstyles.
Airside parking there is a shuttle that will take you directly to concourse B, or A or C. Landside will take you to the main terminal and you'll have to go through the security checkpoint.