To import a new Collection, click on the File button on the top left corner and select Import... (You can also use the shortcut Ctrl+O)
Select the method you want to use:
Choose the item to import and press open:
After the previous steps, Postman will automatically import the collection.
To export a Collection, go to the collections tab in the side menu, then right-click the chosen files and select Export
Click export:
Choose the folder to export and press save: