Invest in finding some great resources that teach you the concepts you have gaps in. I assure you that most adults have holes in their math understanding. That is a result of the poor math instruction that has been taking place in this country throughout history. As a teacher, I had many gaps in my own math concepts. I stumbled on a great Pinterest post which took me down a rabbit hole called Number Talks. This was a game changer for me. I left the pages of my district approved textbook and learned from the National Math Council, Marilyn Burns, and authors who put out great material on Number Talks, math centers, math games and interestingly enough the New York State math modules. These were written in the wake of the Common Core Standards which, is very controversial but, these modules helped me learn concepts I had missed as a child.