Hey Rathnakara.

The National Aptitude Test in Architecture (NATA) measures the aptitude of the applicant for specific field of study, i.e. Architecture. The test measures drawing and observation skills, sense of proportion, aesthetic sensitivity and critical thinking ability that have been acquired over a long period of time, and that are related to specific field of study, i.e. Architecture.

The following link will give you the details about NATA.

https://engineering.careers360.com/articles/nata-application-form

Hope this helps you. Please feel free to respond and ask further questions. 

All the best.