How Do I progress after 8th Grade?

Hi MoonDog,

Typically, a high school student will start with Algebra 1, then move on to Geometry, then Algebra 2, etc. However, this entirely depends on the student's personal learning path. 

You can see all of the math courses that Khan Academy offers at https://www.khanacademy.org/math.
You can also see a list of courses organized into categories by clicking the Courses button in the upper left-hand corner of the Khan Academy site.

I hope this helps!

Am I supposed to just do only Algebra or Geometry at once or do I start multiply at a time?

Most students do one at a time, but that's up to you :)