Hello,

Teacher Eligibility Test is conducted at state level, so first after completion of your 12th standard, you can go through the following steps

Pursue BSc-BEd or BA-BEd as per your stream selection at 10+2 level, this is the best option for a career in teaching, also it saves one year if you choose to go with three years degree course followed by two years BEd, that makes it five years, hence you can choose this course, after passing you can appear for TET or even CTET, you can pursue master's degree later on to become pgt, the best instituion for this course is Regional Institute of Education where admission is done through CEE conducted by NCERT

You can also pursue Integrated MSc/MA as per your stream selection at 10+2 level, and after completion of this course, you need to do BEd

Other than this you can anyway follow the conventional path of doing graduation followed by BEd or master's degree, but the aforementioned steps have become quite popular and as per your convenience you can make selection.

Pursuing any teacher's training program is mandatory, there are courses like DEd, DElEd, BElEd which can be pursued after passing 10+2 from a recognized board, to teach higher classes BEd is compulsory which is for a duration of two years, admission can be merit based or entrance test based, candidates need to pass graduation or postgraduation from any relavant discipline securing 50% aggregate, this may vary as per the norms of the university.