Hey.

To pursue interior designing after class 12th there are various undergraduation courses that you can pursue-

BA Interior Design

Bachelor of Interior Design- CEPT course)

Bachelor of Design (B.Des.)

B.Sc. Interior Design

Different interior design colleges have different procedures for admission. Some of them offer through Entrance tests like CEED, NID, CEPT , UCEED, AIEED etc. 

Best of luck