Hello,
First of all you need to clear your class 12th board exams and apply for engineering entrance exams like JEE,VITEEE,BITSAT,SRMJEEE,COMEDK,WBJEE,UPSEE,..nad many more and then try to clear these exams with good marks to get chance to get admission in their respective colleges.All you need to do is visit their respective websites and check full eligibility criteria and dates of form filling.
After this you can choose civil engineering branch as an option to do Btech course.
Good luck.

Hi,
See first of all after completing 12th you need to get admission in a college which provides degree in civil engineering.
For that you need to give different exams such as jee mains and other private college's exams.
Andyou need to qualify the minimum criteria for admissions too.
After getting in college with yiur desired branch you will have the study span of 4 years aftee which you will get your degree of graduation in civil engineering.
Thanks