The problem is, as I'm sure you'll appreciate, that we can't teach you everything all at once, and sooner or later you'll just have to start on something.
So here are my general suggestions -
Start buying a general magazine like
Airfix Model World or specifically on aircraft or military vehicles, they are the two most popular fields. Just go to a newsagent - W H Smiths is the obvious choice - and see what you like. Though the
Airfix mag is sold in Sainsbury's, I don't know about other supermarkets
As you read you will see how things are done, and pick up tips, techniques, & ideas
Similarly Search YouTube for 'plastic modelling' there will be videos for beginners, or specific areas. Make a start and just keep following the suggestions
Airfix beginners kits might not be the best, but you've gotta start somewhere
As I've posted in other threads,
www.abcbrushes.com do a general modelling set of brushes for about £12 or see what else they have
Knives. - I like scalpels. #3 handle is smaller than #4
www.scalpelsandblades.co.uk have taster sets with one #3 or #4 handle and one of each type of blade for a reasonable price, so you can see what you like and order from there
The most common type of blades are 10, 10A & 11 for size 3 handle or size 18 or 19 and 25 for size 4 handle
Otherwise just search their website to see what's available