Maths self education question

Hi,
I skipped year 11 maths because I was good at it and now I am crap at it. Well to be honest its not just that I skipped: if I was brilliant I could work it out for myself. I’m intelligent in other areas but struggle with maths. I would really like to try to improve this.

Do I have to go back to the high school textbooks or is there a good site or book for an intelligent 20 something who wants to catch up? Basically I like to understand the big picture and my qualm with text books is you never know where any of it is heading. I would like to know what all the different fields of maths are for example.

Thanks.