Hi there!
If someone were to ask if you have any schooling, you'd respond with "I got my master's degree in mathematics from the University of Florida."
"Got" or "get" refers to an act of retrieval on your part. You had to go to the school and study. Using "take" or "took" is used to for an act of retrieval that wasn't earned.
"I took the cookies" versus "I got the cookies". The first one tells you the cookies were not for you to have.
"From" is a preposition referring to placement in space. In other words, prepositional phrases starting with "from" will answer the question of "where".
Using "in" turns the prepositional phrase into a category. Which major? In Mathematics. You major IN subjects. It wouldn't be appropriate for mentioning where you received the degree.
Master's degree wasn't capitalized in this case because it is a general term. If you are mentioning the full title of the degree, then capitalization is require. "I have a Master's of Science in mathematics." The clue here is seeing if the word "degree" is present or not.
I hope that helped a little!