To map a requirement to a test case, perform the following steps:
Navigate to Requirements and select the folder containing the requirement you want to map:
Now you can do one of the following:
Click Map on the line of the requirement you want to map.
Click the requirement name, and then click Map in the Mapped Test Cases section.
On the subsequent page, select the folder containing the test case you want to map to your requirement in the panel on the left, choose the needed test case on the right, and click Save:
Now you can see that the requirement is mapped to one test case:
Deleting a requirement or test case removes the mapping as well.