"Is the word revision only used for exams?"
No. "Revision" is in fact more commonly used to describe versions of work after the first version. For example, "We made several revisions of the original document before we released it to the public."
You have tagged this question with american-english so I assume you're interested in how the word "revision" is used in American English. Having spent the first 21 years of my life in North America, I don't think I ever heard the word "revision" used in association with "studying" for an exam or going over topics with a tutor, until I moved to England to do my PhD. In England, I rarely (if ever) witnessed people saying they were "studying for exams" and instead they would say that they were "revising for exams".
In british-english, you can say "we are doing revision today", even if the revision is not for an exam, but to be more clear you might want to say "we are having a tutoring session", or "we are having a tutorial" or "we are revising topics from last week" or "we are going over the material from last week". In american-english I would recommend the above options which do not include the word "revision" or "revising", for example: "we are going over the material from last week".