The question makes it sound like you've mixed up the concept of event blocks and conditions.
Event blocks contain a list of conditions and a list of actions. An event block can be a sub-event to another event block.
Conditions test whether things are true or false, and the actions run if all the conditions were met. Conditions can be in both events and sub-events, the distinction doesn't matter.
However an important point about sub-events is that they run after the actions of the parent event block - i.e. they are only checked if all the parent event's conditions were true.