Sorry about the particularly broad question. I am an undergrad History major at the moment with potential plans of going to grad school for history and an eventual goal of maybe being a professor. However, I have no idea what it is like trying to pay for grad school in this field. I know that grad students in other fields, namely the sciences, can often pay for grad school by teaching, researching, and TAing during, but I don't know whether the situation is similar for students of History. As this sub is filled with professional historians, I figured you all would have some better insights perhaps than those over at /r/history.
You can definitely TA as a graduate student in history (I did for history and French).
Depending on the department depends on the position. I have seen departments with TAs who assisted professors with large lecture classes and maybe lead small discussion classes (what I did), TAs who worked basically as interns for Journals based out of the department/university, TAs who basically acted as an assistant for an endowed faculty position (endowment provided money for Prof to always have a TA).
I also knew colleagues who TAed for other departments (like Women's Studies, Ethnic Studies, Political Science) especially when they had committee members in that department, or were connected with Gender studies or feminist approaches. And I knew a few people whose TAship was with the university administration; basically doing office work/secretarial work (not the most exciting sounding, but they got free tuition/stipend like everyone else and made some good connections).
Be sure to check with the departments you are interested in; the amount of funding and positions can vary wildly, so just ask and see!
(Just thought to add; I ended up taking out federal loans to help pay for everything; the TAship helped a lot, but never payed enough money to pay rent and buy food. During my masters I also worked at Starbucks, which had great cheap healthcare and helped keep me from taking out too many loans. The PhD was too much for me to continue with outside employment, had to focus on writing/reading, so in that case I applied for scholarships/outside funding- also something to inquire about with the department.)
First off, you may want to check out /r/GradSchool and /r/gradadmissions. These are both great sub-reddits, although there is a very large STEM majority in both. What follows will be from my own experience at two different graduate programs and from what I learned applying to grad schools.
In general, History graduate students can receive funding either through competitive teaching assistantships or fellowships. From the two departments I've been a part of as a graduate student (one for MA, one for PhD), about half of the students have some type of financial stipend along with a tuition waiver. The amount of funding you are offered might depend to some extent on the type of program you enter (is it, for instance, a terminal MA program?). Where I got my MA, I received about $800/month as a teaching assistant. At my current PhD program, it's around $1,400/month. From all of the school's I applied to, I believe the most that I saw offered for assistantships was $21,000/year but it's very rare to see a stipend that high. It's important to note, however, that these stipends typically only cover the academic year (9 months). After finishing your coursework (typically after 2 years), you can apply to be an Instructor of Record, where you teach your own class. Being an IoR pays more than an assistantship. Lastly, there's fellowships, which may be equal to or more than an assistantship. Throughout your graduate career, you'll also be applying for grants and fellowships outside of your department that will help with various costs.
Depending on how much money your department/university has, you may be able to get some academically-related expenses paid for. For instance, the program I'm at has $1500/year set aside for each individual graduate student for research and travel. Moreover, my program will pay in full for any foreign language training you may need. We recently had a student, for instance, spend a summer in Beijing learning Mandarin, and we've had students go to South America and Europe as well. Most departments will also offer to pay a certain amount of money for trips to conferences.
There's a lot of money out there for graduate students, but you will spend a lot of time applying for grants/fellowships/assistantships. The amount of money available will also vary considerably depending on the department and university. These are things that you will need to ask the graduate coordinators at the places you apply to.