It is good that you have set your goal to do a course with ICAR. UG Courses of ICAR is mainly given through various agricultural universities. They conduct entrance examination for selection every year. The ICAR website states the eligibility for appearing the entrance examination:

Must have passed and obtained not less than 50% marks in aggregate for admission under General, UPS and OBC categories,40% marks in aggregate for admission under SC, ST and PH categories in 10+2 examination with PCM/PCB/PCMB/PCA/PCH subject combinations. Candidate having compartment/ supplementary in any subject in 10+2 examination is not eligible for admission. Candidate appearing for 10+2 examination can also apply but shall produce 10+2 pass certificate with appropriate % marks during counseling. Pass in English in 10+2 examination is essential for admission in some of the Universities.
Detailed regulations can be obtained from
http://icar.org.in/files/regulations.pdf

if I understand your question correctly, you are thinking of which course you have to select after you clear the entrance examination.
ICAR provides a variety of courses in UG. Some of them are Agriculture, Horticulture, Fisheries, Forestry, Home Science, Sericulture, Biotechnology, Agricultural Engineering, Dairy Technology, Food Science, and Agricultural Marketing & Co-operation.
You need to select a course which best suits your taste. By the end of your class 12 course, you must be able to make your mind up. All the best.