thanks but how do I go about writing one. are there any websites or something that can help me with this?
Otherwise you'll have to look elsewhere probably (maybe the websites for the unis you are considering)
If you want to apply to UK unis, you do so through UCAS with a single personal statement that goes to all 5 choices you put down. Whatever you do for the US uni will be completely separate from this, and will depend on the uni you're interested in.