Hey! These phrasal verbs are similar, but their uses in certain circumstances slightly differ. For example, you would use 'figure out' when you have solved a problem or come to a realisation. This could be by yourself or someone else has helped you do that work. Some examples: I figured out the answer to the math homework. We figured out why he doesn't like me. Figured out implies that some work has been done to solve that problem or come to that realisation.
For 'find out,' it doesn't imply that any work has been done by the subject. If I said, 'I found out the answer to the math homework', it doesn't imply that I have done any work to get the answer, the teacher or someone else could have just told me the answer. So, you would use 'find out' if you have gained knowledge of something without solving the problem yourself, normally you have been told something. Some examples: he found out that his dog died. Sarah will find out tomorrow that she didn't do well in her exam.
I hope this makes sense and helps you!!