The eligibility for NET is having masters in your subject. NET is National Eligibility Test conducted jointly by CSIR and UGC, after you qualify the test with a high rank, you can get CSIR Junior Research fellowship for your research work for two years and Senior Research Fellowship for the next three years. Otherwise just qualifying will make you eligible for Lecturership in College.
You need to Google or browse through some book shops to find study material for your subject. You can also sit for the NET while doing your Masters, but for getting into research institute or college teaching, you will need your Masters results.
It happens twice a year, in June and December.