Try This:
rem Camera Movement
Do
Cam_YAng#=WrapValue(Cam_YAng#+(MouseMoveX()*.5))
Cam_XAng#=WrapValue(Cam_XAng#+(MouseMoveY()*.5))
Rotate Camera Cam_XAng#,Cam_YAng#,0
If DownKey()=1 Then Move Camera -1
If UpKey()=1 Then Move Camera 1
Cam_XPos#=Camera Position X()
Cam_ZPos#=Camera Position Z()
If RightKey()=1
Cam_XPos#=NewXValue(Cam_XPos#,Cam_YAng#+90,1)
Cam_ZPos#=NewZValue(Cam_ZPos#,Cam_YAng#+90,1)
EndIf
If LeftKey()=1
Cam_XPos#=NewXValue(Cam_XPos#,Cam_YAng#-90,1)
Cam_ZPos#=NewZValue(Cam_ZPos#,Cam_YAng#-90,1)
EndIf
Position Camera Cam_XPos#,Cam_YPos#,Cam_ZPos#
Sync
Loop
That should do for camera movement, except you're going to need to add some gravity. Then shooting, enimies, levels, etc...