Never owned a 4-stroke and need to check the valve clearance and maybe adjust it. How do I do that and where do I measure?

I do not know what the clearance (Lash) should be for your sled but here is how to check it.
Pull the plug, take the valve cover off, slowly turn engine over until you reach TDC both rocker arms should be loose (little wiggle room) then slide a feeler gauge in between the rocker arm and valve stem.
You may want to slowly turn engine over several times in the running direction watch the valves to get a feel where it is in the cycle.
Good luck.

Thanks Shawno, now I just have to find the clearance.

Valve clearance on the Polaris motors is .007 from the factory (both intake and exhaust) It is critital that this is check with the motor at Top Dead Center. This can be verifyed by removing the clucth and the keyway would be at the 11 o'clock position.

Thanks snoxdad, now I can check the clearance. Thanks for the help all.