Is it acceptable for a student to hire a tutor to explain and fix homework mistakes? In a course we have a lot of hard homework. We are allowed to share solutions etc, as long as each student's doesn't just copy but understands what he/she writes.

Is this acceptable to hire a tutor help me solve the homework I can't solve?
We are allowed to share solutions etc, as long as each student's
  doesn't just copy but understands what he/she writes.


This is the only information we have about your instructor's policies, so this is the only answer we can give to your question. It's OK to hire a tutor for help with the homework, as long as you don't just copy but understand what you write.

It's also possible that your instructor intends different rules for paid tutors than for cooperation with your fellow students. However, we would have no way of knowing that from the information provided in your question.

There are also general expectations about plagiarism and originality, and these are ethical norms that you're responsible for understanding and following, regardless of your instructor's policies. Your description of your working relationship with your tutor isn't specific enough to make it clear whether you have a problem here or not. As JeffE has pointed out, "fixing" your mistakes might entail plagiarism, if it means that what goes on your paper isn't actually what you wrote yourself.