Extra-Vehicular Activity
From Kerbal Space Program Wiki
An Extra Vehicular Activity or EVA is when your kerbals trust their lives to the chewing gum, duck tape, and prayers that comprise their (mostly) airtight suit, and exit the capsule to go enjoy a space walk. The Kerbals can navigate outside their spacecraft by moving on ladders, the ground, or activating their personal RCS system. The RCS system does have limited fuel. To start an EVA either right click on the capsule, or mouse over the images in the lower right corner. To re-enter your capsule, get close to the door and press F. EVA's were implimented in 0.16.