Hey Sandhiya.

NATA is among the many entrance exams which are conducted for admission to architecture courses. NATA is an entrance test which is a mode for admission to many and  various TOP colleges for architecture. So even though NATA is not mandatory for admission to architecture courses but it is an important for the course of B arch. Other than NATA there are other entrances like JEE Mains Paper 2 which is also a national level entrance as well as other state and institute level entrances like COMEDK, WBJEE, OJEE, MHCET etc.

Best of luck