Please someone explain this system? I need to understand it

Probably mainly for anyone who lives in the UK, England, because I'm not sure of the differences in British and American education systems. However, still feel free to reply, with any knowledge you have on this or maybe with any good websites or something.

Okay so I am in secondary school (High school) and I'm in year 11. I'm going to be doing my mock exams in December (Mega stress). I've been told that we have to know what colleges and courses we want by the end of the year. And I'm so confused!!!

All I know is that there are A levels, BTEC courses, AS, A2... Don't really know what they are or what they mean though.
I need someone to just explain to me the whole thing bit by bit.

What are all the types of courses you can take? Which ones are better? Which ones are pretty much the same? How many can you take?
What types of courses should I pick if I want to study certain subjects at college and wanna move it into university later? Are there any specific requirements, and what things are favoured over others? (Types of courses or subjects themselves) What is the process?
And what are UCAS points?

Say, I want to go to college and study psychology, sociology, something like art and design. That's all I know so far on what I wanna do. However I am kind of interested in advertising and marketing, but I am bad at maths and business style stuff.
Then, I want to go to university to study psychology/sociology (and whatever other subject I want) further.

I pick those 3/4 A levels... and then what happens?

Someone please explain this to me, I've been trying to search it but I can't find anything easy to understand. I really want to be secure on this, and know what I should do ahead of time.

I hope someone in U.K. replies because I don't know nothing about all this.

Does you school have a career counsellor? They should be able to give you some form of guidance.

Yeah. I have signed up to get an appointment with her about my future education choices etc. It was supposed to be like a month ago (and I even marked it as ASAP) and I still haven't heard back from her. I guess there are a lot of people who don't know what to do, and I suppose I will still have to wait quite a while before she gets to me.
I would try going to see her, but she is always busy and rarely in her office, especially since now we are doing our 'mock interviews'. But good idea, I might try and ask her about it when she sees me eventually.

In the U.S. when you apply to college, you specify your major. You are then accepted or not as that major. But the minute you get there, you can change your major.

So I think that's why they are asking you to declare a major now in high school. It must be a similar system.

But do ask your counselor and don't forget to ask how easy it is to get jobs in the field of interest and what kind of salary you can expect.

Good luck on the exams.

Good luck with your exams