Testing api with postman

I'm new to api test.I have a project to complete but I don't know much about it.I need to use I need to use postman for testing however my teacher also shared java codes with me.There are classes like base class option class in it.I will test - https://restful-booker.herokuapp.com/.I'm watching the postman lessons now, but I don't understand what java is needed for.Can you help me?I wish everyone my best