I'm sure we've all been there, at some point or another..
Anyway, Gateway Travel is essentially company provided travel to and from your residence to your assigned base (as long as your residence is more than 130 miles from your base). The company will provide a positive space ticket and hotel accommodations (at your base) prior to the report time of your trip, but on your own time. Your Gateway airport should be located within 130 miles from your residence, and from what I understand, be on the list of airports that are currently designated as Gateways (approved by the Company and Union).
There are tax implications to utilizing the Gateway airfare, and I'm sure other details.. but that should give you the picture.
Oh yeah, I think I recall you mentioning that you live in the SanFran area.. I believe SFO is on the list.
Again, I do suggest you take some time to page through this thread, as there is some great information - the good, the bad, and the ugly. I think it's all beneficial if you're serious about working for Atlas.
Time for a beer?
Cheers..