hi,

there is no specific marks criteria is applicable for st, you may appear in sat exam if you are in final year of your 10+2 course, sat conducts 7 times in USa AND 5 TIMES IN A YEAR IN OTHER COUNTRIES, so as per your country you need to check the exam date and schedule, sat exam is the entrance test of admission in united states colleges in various disciplines, It is also accepted in colleges in Australia, the United Kingdom, Singapore and Canada. you need to register in the official website of collegeboard  (//collegeboard.org) for sat exam registration process,

https://collegereadiness.collegeboard.org/sat