there are many websites about this but there should be an offical one for the us, for Uk I know you need birth certificate,passport, any divorce papers if previously married and police check, also lots of proof that you have met each other, like photos,reciepts, tickets for traveling. You might also need bank statements. Good luck I am doing the same but trying to get my fiancee to the uk, It takes a lot of planning and is better to make sure you have everything you need now.