Once you have successfully landed you can explore the surface with an EVA. Selecting the 0 key will bring you to floor looking out the open hatch.
The most realistic way is to move toward the hatch. Now turn around and back out the hatch and down the ladder. That's one small step!
If you are using the Keyboard / Mouse as your primary controller then the commands are as follows.
If Keyboard / Mouse is the primary controller, the A,D,W,X commands can be used to 'walk'. The mouse is the camera angle.
Make sure you plant the US flag at an appropriate position by pressing F.
The joystick Point of View (POV) hat - if you have one - will allow you to 'look' in the direction you desire. Movement of the joystick will walk you in that direction.