When can I use 4wd?

You can use 4wd (4x4 Hi/Lo) whenever you need additional traction when accelerating - 4wd will not help you stop in slippery conditions. You can safely use 4wd on sand, snow, ice, mud, etc. - do NOT use on dry pavement or even in the rain. Your drivetrain may bind and be damaged if the wheels cannot slip to relieve tension.