In response to the original poster, no, it's not a stupid question! Few of us were born around boats, grew up with them, come from generations of sailers. A lot of this stuff is non-obvious, confusing, counter-intuitive, or just plain obscure.
I am going to guess that your C22 is an older model, and that while you've cleaned it very well, that the gel coat is heavily oxidized. This makes it porous, and that's why dirt that hits it stays and even appears to stain.
To make the gelcoat so it won't stain, one need polish it. For a heavily oxidized gelcoat, this involves wet-sanding it through increasingly fine grades from about 600 to 1000 or 1200 or even finer. After that, you compound it, then polish it. The, to protect the new finish from UV and contaminants, you wax it. MaineSail has an excellent tutorial on this for a boat's topsides in his sub-forum on this site.
(As an aside, for reference, 'topsides' is the part of the hull from the waterline to the gunwhales, i.e., the sides of the hull. The part you walk on and other generally horizontal parts of the top of the boat are the deck, more specifically the deck, coach roof, cockpit sides, cockpit bulkhead, and so on).
On deck, there are both smooth and non-skid surfaces. Both are made of gel coat (on un-painted boats). The smooth surfaces should be treated just as the topsides, and yes, waxed. There may be products out there that will provide the UV and contaminant protection without being slippery, but I don't know any. The non-skid surfaces can't be sanded or polished as the smooth parts are, but they can be cleaned and they should be protected. There are waxes made specifically for non-skid, such as Star Brite non-skid wax, Woody Wax fiberglass and non-skid wax, Marine 31, and so on.
If all else fails, if your gelcoat is too far gone to bring it back on its own, you can always paint it.
