This is the information on the Kent CC website: https://shareweb.kent.gov.uk/Documents/education-and-learning/school-education/applying-for-school/Admission%20to%20Secondary%20School%20in%20Kent%202014%20book.pdf
As with any area (if you are currently in East London, are you also applying in Essex?), most GSs are likely to be oversubscribed, so it is important to look at the oversubscription criteria for each school you are interested in applying to. I assume that you either have visited or will be visiting them?
I have no idea how Kent CC presents the results of the Kent Test with regard to advice, but last year in Essex, the CSSE gave advice as to recent lowest scores achieving admission to the various schools, and how "safe" various scores were.
As for the actual application for a place, this is by naming all the schools to which you wish to apply on the CAF (Common Application Form) supplied by your home local authority, wherever in the country the schools are, and in your true order of preference.