It depends very much on the class. Mostly I TA sections for large (500+) survey lectures (I'm scheduled to teach my second class as instructor this summer - yay!); I don't know if you have those in Europe. They usually fill a GER, and that means you get a spread of students: Freshmen who never had a class before, seniors who just realized they need a GER to finish, and then some students who are genuinely interested.

I've TAed all of our World History courses (11000 BC-Present) and Western Civ courses (1000 AD-Present), and a lot of Greek Myth, so more often than not I'm working with material I'm not too familiar with (I'm pretty good with Myth - WW2 not so much), which is actually really fun. The assigned primary sources are usually straight forward, and when things go well I'm there not really to be too active - ideally the students would just sit in a room for an hour and discuss the texts themselves, but reality, right? - I talk the students through the assigned texts (by which I make them talk me through them) and show (again, get them to show me) how the assigned texts are related.

If the students have done the reading and are willing to participate, it's really fun. Engaging with the students is cool, seeing learning accomplished is cool. As a matter of fact, my favorites are C students who want to do better. As don't need me, and other students just aren't trying. Even when students completely misunderstand a text (and incredibly often students read a text and take the exact opposite of the intended meaning from it), walking them through the argument of the text and helping them understand what's going on in it is rewarding.

On the other hand, sometimes groups of students come without having read a damn thing, and it becomes habitual. Total refusal to engage with the course. Those sections are just torture. They wreck my self esteem, they eat of tons of energy as I try to figure out how I am going do class next time, they basically make me hate life. Is this happening because I'm a bad teacher? What can I do to fix it? Myth is the worst. I go into Myth sections wanting to talk about psychoanalysis or sexual politics or experiences of war or the hero cycle or all kinds of things that require the students to have read the texts, and I find out they just want me to tell them the stories. Sigh.

These aren't isolated students - you get good and bad students in almost every class. Sometimes the whole class picks up an attitude, both good and bad. Getting a section go bad on you is just the worst. I remember one 8AM section I had where I absolutely could not convince the students to read anything. One morning I just gave up and straight up asked them what I could do to make them participate, and one kid in the back said "bring us coffee." I'm not buying 30 students coffee, so I took them to a coffee shop next time. No improvement. Someone in their eval of my teaching that term wrote "LegalAction is too hands-on. He should just let us fail." Worst feeling ever.

I'm friendly with several of my old students, and many of them take multiple classes from me. That's pretty cool (and good for getting a section on your side - "Now, I know that quiz schedule looks scary, but Jessica was in my class last year. It wasn't so bad was it?" "No, it's really not." A little manipulative, because Jessica is never going to say to my class in front of me "It was hell," but it keeps people from complaining).

Sorry I can't help you with the British system admission requirements.

This might be a bit late. I'm not a history teacher, but a modern languages teacher, but I did lots of history in school and uni and loved it like you!

You're doing Nat 5 right now, right? You'll need a N5 in English and Maths. Then you'll need 4-5 Highers. If you want to go to a uni like Edinburgh (where I went) five good highers will do it, other unis in Scotland will accept 3-4 topped up to 5 in your 6th year.

After you finish your 4 year degree, you'll need to apply to do a PGDE to become a teacher.