I think you are already doing the most important thing. That is being open to learning about being a doctor, understanding why being a doctor is right for you, and understanding what the steps are to get there.
There are lots and lots of websites out there which can help lean about the process and what you will have to do to apply.
Actually one of the most helpful things you can do is make yourself a calendar and plan your year a bit. It's sounds a bit extra, but because the summer of year 12 and the first 2 terms of year will be so full on, it's good to plan what you will need to do and work out for yourself when you will have to do things.
Work backwards from the uni submission date of 16th October. Have a think about when your school deadline might be. Often it can be mid-Sept or poss before. So you will need your application finished long before the deadline. So block out some time to do your PS. What needs to go in it might have a strategic answer dependant on where you apply.
When is the BMAT? If you were going to do it, what sort of time would you need to revise?
When do your summer exams in year 12 end. What happens then. Any commitments over the summer? When are the UCAT dates, when would be a good sort of time for you to do it given everything else? If so, when would you have to start your UCAT prep? 6-8 weeks before ? What do you think?
You may decide its better to try and do your UCAT early so that you can be strategic and target your PS. You may get a fab score and decide you don't want to do the BMAT anyway. It may be the other way round and you may need to go full on into BMAT. Plan it out a bit. When (roughly) might you need to register to book both exams?
So no you know when the immovable things are (and exams and doing well at school is part of that as strong predicted grades are often helpful), then think about some of thr more flexible things.
Like perhaps would you like to put some effort into online work experience like BSMS online, or Observe GP?
Are there any summer schools or other widening participation schemes in your area that you could apply for? When are they, when are thr application dates. Do some research. Nothing as annoying as finding the best thing and then finding you missed the deadline.
Then also think about volunteering. Frustratingly the opportunities to do this may be limited by your age. In any event, it can take a very long time to organise. As can face to face work experience or shadowing. Does your college or local heath prover have any careers support or similar that can help you?
Applying to medicine in the UK, is a bit of a slog and it takes many people more than one year to get a place. You are doing well to think about it this early. The other thing is that it really pays to be strategic. This is dependant primarily on your UCAT, but also on your GCSEs as well as your A levels. So don't get too tied into any one med school at too early a date. That said, if you have a local one and they run local schemes to support medical admission absolutely look at those and when and how they work.
So, you can't tell where you can apply, but a bit of digging around can tell you where, based on your GCSEs / A levels you cannot apply. For example some med schools may request certain grades in specific subjects. If you haven't got them then that's a non starter. You can set up a spreadsheet and look at which med schools there are. Whether they run undergrad, grad or gateway courses, and whether they are UCAT or BMAT, and whether you have the right GCSEs for their current admissions policy. This may help you winnow them down a bit.
Then once you have a list of possibles have a closer look and dig around on their websites what are they looking for, what do they say about work experience, what do they suggest etc. Then this eill give you an indication of some of the other things you may need to fill in over time. Which ones of the "possibles" will be your strategic choices will be something for after you have your UCAT results. The TSR which med school megathread will help you with that when you need it.
But for now, plot out the year ahead. Take time to lean thr process and educate yourself about the options.
Primarily though year 12 is for working hard on your academics and having a bit of fun !
Apologies for the long ramble and good luck.