replacing roof shingles and install help?

what do u need to replace roof shingles and how would u install them?

Scrape off all material down to the roof deck. Make any repairs needed on the deck. Install new tar paper base. Install new flashing. Install new shingles.
It depends on whether or not there are two layers on the roof now. If there is only one, you can shingle over it in most areas. If there are two or more codes usually require removal. If you remove the shingles, you need to check the underlayment to be sure it is solid..replace if not..then re-felt it, flash it and put on new shingles. It is worth renting a roofing stapler/nailer if you are doing this yourself. Roofing is not complicated..but it is hard work. The key is getting the first course straight, then paying attention to keep it straight. Most home centers can give you tips if you have not done roofing and you buy the shingles from them
answer to #1 A roofing contractor........because if you are asking this then it is definately not a DIY project. answer to #2 A case of beer and a lawn chair to sit back and watch.