Having your "VR legs" refers to being comfortable with long, usually loco-motive (traditional movement without teleporting) sessions without feeling nauseous. While it doesn't happen to everybody, VR can make people feel a bit sick the first time they try it, and it can take several hours of intermittent use with the device to acclimatize yourself to this new style of gameplay. Once you have done, you've acquired your VR legs; you should now have no problem walking around with the left analog stick and controlling the camera with the right as you would in flat screen gaming.