Try here for pics and a few instructions.

I don't usually cover anything. I don't just pop the hood and start blasting water all over the place either so there isn't much need to cover anything. The only place I ever spray water on directly is around the painted areas like the wheel wells and firewall. I don't use high pressure either. Use a good degreaser to loosen up the crud and then the water just rinses it off. Don't rely on high pressure to do the work for you. Use good degreaser and get your hands dirty. If you get your engine clean once really good then you don't have to worry much about keeping it looking that way. Just touch it up once or twice a month and it will be fine.