Historians are people who study and write about the past, not just casually, but on an academic level. They've likely studied for it at a university, perhaps specialiizing in region or timeframe. But the majority of these people do not get a job that's purely being a historian, which is 'researching and writing about the past'. Because there's not a lot of money in that, unless you're a good enough writer to write great books.
Many, very many are teachers, either at high schools or universities. Especially the latter gives them time and resources to continue their research while teaching the next generation. Another full-time job for historians is archaeology: the people who go to digsites and oversee the work and dig up all kinds of nifty stuff. Some historians become authors, although this is probably quite rare as a real avenue of revenue. Publishing books and gaining enough profit off that to live from is quite difficult. Then there are those who work in museums, for example as curators. The people who organize the exhibits of historical things. Then there are art-restorers who take ancient (and probably also modern at time) art and try to repair damage done to them. Archivists at highly acclaimed libraries are often highly educated individuals who understand how to research topics. Historians fit the requirements for that position perfectly.
All the above mentioned jobs are directly related to history, but I am fairly certain that most historians do not have jobs that directly relate to historical research. The positions are few, the people are many. Researching history provides you with a lot of useful tools that can be applied in different jobs however. Reading and interpreting texts day and day out, writing essays every other week, makes most historians well-suited for any job that requires lots of reading and writing. Think of editors or writers at magazines or newspapers. And most historians are well versed in several languages making them perfect candidates for jobs that require interaction with people from multiple nationalities, or perhaps as translators. I also believe there are quite a few historians who become politicians, which requires some skill in rhetoric. The options are endless.