Indian Foreign Services is one of the many administrative positions recruited through UPSC exam. The basic UPSC eligibility criteria applies here as well. You need to have a Bachelor's degree in any discipline to be able to appear for UPSC. As you are in your 11th, you should pick up Political Sciences or Humanities as your subjects in your 12th if possible but certainly in your graduation. Because if you study these subjects along with your boards and Degree exams, you will be ready to appear for UPSC.