Try the US History course and see whether you are able to follow it.  The course starts with the Columbian Encounter and goes forward through time.  There is a good chance you will be able to understand the material, even at a 7th or 8th grade reading level.  Remember that you can always ask questions.

For Science, try the Biology library (https://www.khanacademy.org/science/biology).  You may be able to work with the Biology library and High School Biology together.

What about math and language arts? I apologize for aaking so much, just they are aaking 6 grand for 6 months of rutoring and id like to start myself into learning the basics from 7-8th grade up to 12th within all subjects, i just know that some of the subject courses are for people already in high school, as well also college

For Math, try going to the Sixth Grade course and taking the Course Test.  If you do well, try the same for Seventh Grade.  If you don't do well, try the Unit Tests.  If there are Unit Tests that you don't pass, study the material in that unit and re-take the test.  If it is really not going well, work backward until you are comfortable.

For Language Arts, start with Grammar (https://www.khanacademy.org/humanities/grammar).  The grade-level courses are all still in Beta testing.  There aren't unit test available.  However, you could take a look at the Sixth Grade, decide whether that is where you are comfortable and move forward or backward from there.  (I didn't find the Language Arts courses particularly long.  You could always start with Second Grade and work forward.  No one will know.)

Thank you, cause after the bew year i plan on doing 6-10months of studying as well getting a tutor to help me out before i move onto GED classes

I appreciate the reply as its where i will be looking at to start first

I wish you all the best on your GED journey.  I think you have an advantage as you are thoughtfully planning your course of action in studying.  Good luck to you!