Hey Ridhi,
BCA or Bachelor of Computer Applications is a three year full time graduation course divided among 6 semesters.  People who want to build their career in the field of computers and Information Technology can opt for the same.

Best Colleges in Delhi are:-
1. Institute of Management Studies(IMS), Noida
2. Institute of Information Technology and Management.
3. Indraprastha Institute of Technology and Management(IITM)
4. Chanderprabhu Jain College of Higher studies and school of law
5. Amity University, Noida
6. IGNOU University
7.Jamia Hamdard University
And many more

Every college has its own criteria or selection process In some colleges there are admission on Merit Basis, some Entrance Exam and some colleges there are direct admission.