50cc is the first and least fast engine class in Mario Kart Wii. The low speed and difficulty of the CPUs makes it a great class for beginners in Mario Kart to start with. Only Karts at first can be used in it. Only 2 Nitro Grand Prixes (Mushroom Cup and Flower Cup) and 2 Retro Grand Prixes (Shell Cup and Banana Cup) are available in it at first, but the others can be unlocked quickly if you beat them, so don’t worry.
Speed isn't much of an obstacle in 50cc, so turns are relatively easy to make (so Off-Road stats don't matter much unless you suck at steering). Laps are completed with longer times, so it takes longer to beat cups in 50cc than 100cc/150cc, yet easier.
The non-playable Characters in the courses are set on an easy level to beat. They don't have bad driving skills (like running into walls and such), it's that their karts go at even slower speed than normal 50cc. Item usage is about the same, though.
When it's first played, 50cc is only open to Karts- no Bikes at all. Karts have better Drifting and Handling than Bikes, so it's actually better that the player uses them anyway. However, after all 50cc cups have been beaten with a 1st place, you are now given the option to choose Bikes on it as well… simply press + on the 50cc icon, and you get them.