I basically no know math past 5th grade, and even lack mastery in some earlier topics. What I'd really like to do is go through all the math step by step, however long it takes. 

What is the best way of doing this?

I just chose a couple of courses, hopefully in an order that makes sense (4th, 5th, 6th, 7th, and 8th grade) as a start, but as an adult learner, is there a different way I should going about this? And what are the natural steps after I complete these courses – I'm not from the US so I don't have a good grasp on math terminology (e.g., what calculus etc is).

Thanks!