A great place to start if you've always told yourself that you are 'rubbish with numbers', or you would just like a refresher of the basics, is this free 24-hour course from the esteemed Open University. You even get a free statement of participation on completion. https://www.open.edu/openlearn/science-maths-technology/succeed-maths-part-1/content-section-overview?active-tab=description-tab

A recommendation for a book that has been around for a long time because it is very very good...