I am so confused on what to do for my education. Where do I start?

I'm 15, and I've been "homeschooled" since grade 2

The only subject I did was math on Khan Academy, which is funny seeing as I'm still pretty shit at it

That was it. Nothing was tested, not many actual progress checks. No structure

My mom says that I'm going to do exams this year and I have no idea what that entails or what to study for

I have never done exams before

I'm trying. I really am, but how do I start working on something when I have no idea how it works

Please tell me how to dig myself out of this hole I was put in