The weed & feed will have killed off the moss and turned it black. You can rake the dead moss out and if there are bare bits, then you may need to reseed those bits. There are patch remedies available in garden centres. I haven't used them, but I've seen them. Maybe someone else could advise on these?

Its meant to turn black. That's the weedkiller at work. Eventually you can rake out the dead areas and if it looks very bare you can returf or reseed them.

You say you used Weed and Feed - did it contain a mosskiller as well? These are usually labelled Weed, Feed and Mosskiller rather than just Weed and Feed. If the blackened areas are not moss or weeds, but grass, and the product was a granular type, you have burnt the grass by overapplying in the black areas. If that's what you've done, there's nothing you can do but wait for 6-8 weeks, then see if there's any regrowth of the grass - if not, seed the areas, but don't do it before 6 weeks has passed - granular products take this long to completely break down and disappear.

I thought that you had to water it in after 3 days if it hadn't rained so as not to burn the grass.

Yes, that's right, Cammomile, but if you over apply it, it burns the grass anyway. Often happens if you overlap with a wheeled applicator.