Hello Sanchita,

Portifolio is not the mandatory thing but the most important thing for interview .Because  portfolio is the thing that  make a good impact in the mind of interviewer before your verbal. 

On the other hand, you can  make a portfolio by considering few points as :

• A brief introduction about you, your profile, achievements, especially something that tells the interviewer about your design interests through either cover letter format or even personal statement
• Also, make sure to show a full range of abilities, including sketching, rendering, digital sketching/painting
• Any of the works made using Photoshop, finished products, photography, 3D-modelling, written documentation, 
• Water and oil color paintings
• A collection of some best captures taken by you (photographs) or any other alternatives, 
• Design case studies.

You can go for different design by searching them online or from some good professional portfolios sites.

Hope it helps .

Thank you :)