A level action is one sentence: when a member is added to X, add them to A, B and C.
That one sentence is how a bundle hands out its parts, how a trial ends, and how an upgrade moves somebody. A trial is when a member loses Trial, cancel their Pro after seven days. An upgrade is when a member is added to Upgrade, move them to Pro.
Where they live:
The Level Actions tab lists every rule you have, in plain English. Each level's own edit screen also shows the rules that watch it, with a button to add another.
What sets them off:
A rule fires for every join or loss, whatever caused it: your own checkout, a marketplace sale, the API, an administrator adding somebody by hand, or a registration form.
They never fire during an import. Migrating ten thousand members should not set off ten thousand bundle rules, so it does not.
Delays:
A delayed action is queued and run by the daily job, or by Run Due Actions Now if you do not want to wait for it.
A delayed added rule is skipped if the member no longer holds the trigger level by the time it comes due. That is the detail that matters. A refund inside the delay window never hands out the reward.
Pausing and deleting:
Pause keeps a rule but stops it firing, which is how you switch a bundle off for a week without rebuilding it afterwards.
Delete never touches levels members have already received. Nobody loses access because you tidied up a rule.
Coming from WishList Member:
Your existing bundle relationships are imported automatically along with the levels, and marked as imported, so you can see at a glance which rules came across and which ones you wrote.