You will need to look at and follow the UK immigration site. Arduous but it lets you fill in all the required info including uploading the required documents. I did it last year for my girlfriend and we came to UK for 2 months. Get all your details listed and prepare the two files you have plenty of time and good luck
Try opening a bank account back home , UK in my case. Then try to take out £5k in cash, you will be asked all sorts of questions so B4 you criticise look at it carefully they are trying to combat fraud.