Now that you have been offered a place you will receive information about accommodation. There will be a number of options, locations and prices. Some may have catering and will cost more, and some will be self catered and will be cheaper. Prices for accommodation for a London college will be much higher than anywhere else in the UK. Do some research and use google maps for street views. A good place to find reviews from other students would be TheStudentRoom (link) or StudentCrowd (link).
You will have to rank your choices and you are not guaranteed to get your first choice. There will be an application deadline date so make sure not to miss it.
Once you have been allocated accommodation you might be able to track down other dorm or house mates, and some colleges might make this easier than others. My daughter found a Facebook page townhouse she was staying in, and posted her house number. She soon received messages from other students in the same house.
My daughter’s townhouse (link) along with 4 other students, each had their own room. Two bathrooms (1 up and 1 down), kitchen and dining table. Laundry facilities are on site, and Wifi is included. Annual cost for standard room is £4,441.34 ($5,699). My daughters Federal loan of $5,500 covers all but $199. My daughter and her housemates are moving into a rented house for year 2 and 3, which can be cheaper than a dorm.
If all goes well you will receive an email from the college telling you it is time to enroll sometime in early August. This when you will be uploading a photo for your student ID card. You will find information on what to expect on the first day of arrival including picking up keys and moving into your accommodation. York St. Johns had an online scheduling tool that allow you to pick a date and time of arrival. I guess they do not want all the student and parents arriving at the same time.