What you do as a historian will depend on the type of job you take on; while many historians become professors (academia), others pursue public history (working in libraries, museums, and archives). The private sector also employs historians; one primary example is in construction where a cultural resources specialty may be called in to ensure historic sites are preserved (they have to confirm with the National Environmental Policy Act [NEPA]). I can address the first with some more detail.

If you take the academic route (professor), your workload will depend on the institution you work for. If you're at a community college, expect most of your time spent lecturing and grading. Generally that means five classes a semester with each class being three lecture hours a week. Preparing lectures can take up a bit of time, especially the first time around. Depending on your position in your department, you may be able to select which class you want to teach and when to teach them. For example, if you're new, you may have little in terms of choice, sometimes even teaching course that may not be your original field of study. There is also a push for more online teaching, so you may also be working remotely and have to establish an online course (discussion boards, audio/video, etc.).

If you're at a four-year university, you may have graduate assistants do some of your lecturing and grading, but also have to give graduate seminars and serve as advisers on graduate committees (overseeing graduate research).

Publishing papers and books is also something many academic historians do, but the obligation varies. Four-year universities will put a higher priority on professors publishing than community colleges. With that in mind, some degree of grant writing will be part of your work to securing funding for your research. You may also be attending conferences to present your research, but also to see how the field is developing. You may also have departmental and institutional commitments (serving on committees for different academic programs).

For more information on what historians do, the American Historical Association has many resources on what you can do with a history degree here.

I’m a recent history graduate so fit into the historian category. I myself am now doing a masters and many of my cohort have gone on to do similar. I myself as the other post has said am going into academia and publishing articles. In fact my dissertation is being published.

The title “historian” although we are historians is open to interpretation but ultimately we do gather and analysis information from the past and in some instances protect documents, buildings and other items for future generations.

I view my job as a historian to learn from the past and to ensure the mistakes don’t get passed on. Additionally I view it as passing information on to future generations so important lessons aren’t forgotten. If one takes an example something like the holocaust I deem it my job to protect and preserve details with respect to this for the memories of those who sadly perished. So I guess my actual job as a historian myself is protecting items from the past for the future and making sure that they will be available for many many years to come.

That’s myself as a historian just saying what I myself do as a historian.

The subreddit FAQ has a special section about history as a vocation. There are also interviews with various flairs on the AskHistorians Tumblr page, where the interviewees talk about their offline scholarship a bit. /u/tenminutehistory spoke in a podcast episode about life as a(n) historian and during another one about historiography and historical epistemology.

EDIT:

/u/mikedash has also answered What is a historian?