A bug is an error or fault in a tested program that causes an incorrect or unexpected result or behaves in unintended ways.
A custom field that keeps a handle to the "parent" Test Case.
A custom field where you can describe an environment where the tests are executed.
Add to structure
That operation allows connecting the current Bug to any Test Case, even if it has other bugs connected.
Disconnect from structure
There is also a possibility to detach a Bug from the structure. Choose that option will require your confirmation.