If you haven't installed Postman yet, check Installing Postman.
Once you have installed Postman, your screen looks like this.
1. Click on the "+New" button, to create a new request or Collection.
Click on Request option to create a new request, enter a request name.
2. Your new request tab looks like this, It has options to select your method, textbox to enter URL, and tabs to specify params, Headers, test scripts etc.
2. To create a new collection, click "+New" again and select collection option from the available options.
3. Enter a collection Name and click "create" button.
4. Your created collection looks like this under New Collection tab. Click on the collection name and select "Add Request" option to add a new rest request.
Enter a request Name and click "save to Deckofcards" button. where DeckofCards is the collection you have created.
You can now see, the requests added under your collection.
5. In your request tab, enter the endpoint in the textbox and hit send to see the response in your response tab.
Here, we are using a public Rest API,
https://deckofcardsapi.com/api/deck/new/
Congratulations!!! you have created your first test request in postman.