Nvidia will hand you a digital copy of Rise of the Tomb Raider when you buy a select GeForce video card.
Those who purchase a Nvidia GeForce GTX 980 Ti, 980 or 970 graphics card or system, or a participating GeForce GTX 980, 980M or 970M notebook - you'll get the game free.
Participating retailers and online stores are listed in full here.
If purchasing elsewhere, you should make sure the retailer is offering Rise of the Tomb Raider as part of the package, obviously.
Rise of the Tomb Raider will be released on both Windows 10 and Steam January 28.