All are re-mappable, but by default the left cluster are Esc, Shift, Alt and Control, the right five are for Top, Front, Right, Rotate 90 Degrees, and Lock Rotation, there’s a Menu button meant to call up the 3DConnexion GUI thing, a Fit button, and four multi-function keys across the top. Here is how the could have made it more perfect:

https://www.amazon.com/3Dconnexion-3DX-700040-SpaceMouse-Pro-Mouse/dp/B006GPZ17K