In order to appear for SAT 2020, you need to create a college board account through the official registration link. Then you need to fill the application form and select the available center and preferred date of your choice to appear for the exam. To know about the various SAT subjects click the below link
I hope it helps.
Go through the Collegeboard website.
Look for the test dates.
Then register for the test on the same website.
You'll receive a confirmation page/mail in your e-mail id.
Maths: Problem Solving and Data Analysis, Advanced Maths, Algebra
Reading: Understanding the passages from US, History, Social Studies and Sciences.
Writing and Language: Expression of ideas
All the best for your exam.