REST(REpresentational State Transfer) uses various representations to represent a resource like Text, JSON and XML. JSON is now the most popular format being used in Web Services.
Postman uses various HTTP Methods.Some of the commonly used HTTP methods used in Postman are as follow:

GET − Provides a read only access to a resource.
PUT − Used to create a new resource.
DELETE − Used to remove a resource.
POST − Used to update an existing resource or create a new resource.
1)Sending the API request

1.Enter dummy-api.com/get into the URL field.
2.Hit the Send button to send your request, and you will see the server response in the body with some JSON data.
3.Postman will dummy-api.com/get under the History tab of the sidebar.

2)Creating the collection

Collections are groups of saved requests

1.With the request you just created in the request builder, click the Save button to open the SAVE REQUEST modal.
2.Request discription is optional.
3.Now, save this request to an existing collection, or create a new collection by entering a collection name, and then Save.
3)Managing the Environments

Environments give you the ability to customize requests using variables. This way you can easily switch between different setups without changing your requests. Environments can be downloaded and saved as JSON files.

Create a new environment

1.Click the Environment option in the upper right corner of the Postman app and select “Manage Environments”. Click the Add button to create a new environment.
2.After creating the environment you can share,download,edit,duplicate and delete the environment.

4)With Postman you can write and run tests for each request using the JavaScript language.

For example:
var jsonData = JSON.parse(responseBody);
postman.setEnvironmentVariable(“Userid”,jsonData. userId);

//This parses theresponse body and assigns the value of ‘userId’ in the response data by creating an environment variable: ‘Userid’.

var schema = {
“items”: {
“type”: “string”
}
};
var data1 = [jsonData.name];
console.log(tv4.error);
tests[“Valid Data1”] = tv4.validate(data1, schema);

//Checks if the name is string.
Similarly validates the entire response schema.