Swirl marks are actually just very fine, very shallow, very hard edged little scratches randomly scattered throughout the paint. The harsher the light source illuminating them, the more they stand out, which is why a black car parked in the shade can look great but as soon as you pull it out into the sun it looks horrible.

Glazes like this Malco product, Meguiar's #7 Show Car Glaze and others do a great job of filling these in and hiding them, but they tend to be very short lived products that will actually wash off quite easily. They also tend to offer almost no protection at all. It's always best to apply a good wax or sealant after using any glaze, unless you're using the glaze just for some added "pop" before a car show. Glazes also have their limits - they can't fill in everything.

I would recommend you give Meguiar's ScratchX a try. It takes some serious elbow grease to remove swirls by hand, no matter what product you're using. The biggest mistake most people make when trying to remove defects by hand is to just wipe a polish on and then wipe it off. That doesn't cut it. Take a look at THIS THREAD from the Meguar's forum showing what can be done with ScratchX by hand. It's a real eye opener.