Shared steps
A shared step is a block of steps maintained in one place and used in many test cases. "Sign in as a returning customer" is written once; the forty cases that start with it point at that one definition.
Creating one
Settings → Shared steps → Create. Give it a name and the steps it contains, exactly as you would inside a test case.
Using one
In a test case's step editor, insert a shared step instead of writing a new one. It renders in place, in order, marked as shared so a reader can see the block is maintained elsewhere.
What changes when you edit one
Editing a shared step changes every case that uses it, from the next time each is read. That is the point, and it is also the risk: a shared step used by forty cases is a forty-case edit. The screen tells you how many cases reference it before you save.
A bug hunt's copy of a case follows the library's steps, so a shared step edited today shows its new words in every hunt holding a case that uses it, the next time that case is opened there. Results already recorded on the step stay.
When not to use one
If two cases share three steps by coincidence rather than by meaning, leave them alone. A shared step is a statement that these steps are the same thing and should change together. Extracting every repeated pair produces a library where no case can be read end to end without opening four other records.
Availability
Shared steps are available on every plan, from Starter upwards.