How to write test cases (self study)

hello all, i am trying to learn on my own how to write test cases. I do not know how to start? How do i start writing a test case for the following scenrio?

—>verify the behavior of the UE when the network fails to set up an EPS bearer or if the EPS bearer is deactivated.
(3GPP TS 24.301 Network Initiated ESM Procedures)

another question is, is every test case found in 3gpp conformance testing document.