Apply for a provisional licence - this lets you take lessons and book tests - you can apply online but will prob need to send them some ID.
You'll need to sit and pass your driving theory test at a test centre, some people like me do this before they take any driving lessons just to get it out of the way, but you need this pass to book your practical/final test
Arrange driving lessons - imo ask people you know to recommend a good instructor rather than random online schools, you will learn in their car on their insurance and in the vast majority of cases you will sit your test in this same car and insurance and won't need anything extra. If you want to go through the hassle of buying and driving your own car for a test that's more complex, likewise if you want to take lessons from a parent or whatever you'll need to make insurance arrangements
All going well after 30+ hours on average you should be reasonably confident to book and sit your practical driving test. Prepare as best as you can but it's pretty normal to fail as it's an pretty unforgiving test (took me 3 tries for both my theory and practical)
Costs monthly can honestly vary wildly, insurance will likely be your biggest as a new & young driver, deffo get insurance quotes for cars before you buy them as you might get nasty surprises that make little sense to you, but as a ballpark figure for insurance, tax, MOT and servicing you're maybe looking at £2-3000 a year with insurance being maybe 2/3rds of that, that's just a guess