Controls

When in a flight scene with a craft containing Kerbals, press C to switch to the internal view, then press Y to get out of your seat and explore your vessel in IVA.

Right-click to toggle mouse look. You can left-click on hatch handles and seat buckles to interact with them. Left-clicking handrails while seated will also unbuckle.

In a centrifuge, press the Jump key while touching a railing or ladder in the rotating section to enter artificial gravity mode.

Alt-G will toggle gravity if you get stuck.

These can be customised by editing GameData\FreeIva\settings.cfg.

Keys	Action	Setting Name
Y	Get out of seat (unbuckle) while on IVA	UnbuckleKey
W	Move forward	ForwardKey
S	Move backward	BackwardKey
A	Strafe left	LeftKey
D	Strafe right	RightKey
X	Toggle Crouch	CrouchKey
Space	Jump	JumpKey
Q	Roll counterclockwise (when in low gravity)	RollCCWKey
E	Roll clockwise (when in low gravity)	RollCWKey
Left Shift	Move upwards	UpKey
Ctrl	Move downwards	DownKey
F	Open or close a hatch that you're looking at	OpenHatchKey
C	Return to original seat
Alt-G	Toggle gravity
Alt-Left-Click	Grab or throw prop
Left-Click	Use prop

This uses the Unity standard names, so if you want to use buttons on joysticks, mice or other hardware, see here for the list of correct names: http://docs.unity3d.com/ScriptReference/KeyCode.html