You have some conditions, which are about states of your devices. You make a logical rule with those conditions. That rule is either true or false, depending on the states of the devices and the evaluation of the rule. Some rules are very simple, for example, Motion Active. A single condition makes for a simple rule. Some rules are more complex, for example, Door Open and Temperature < 50. A rule for that might be Door Open AND Temperature < 50.
Any time the state of one of your conditions changes, for example, Motion goes active, or the Door closes, the rule will be evaluated with the currents states for the conditions. At that moment, the rule is either true or it's false. For example, if motion became inactive, a rule that is Motion Active would become false. It motion became active, the rule would become true. If the Door opened, and it was 60°, that rule would be false. But if the Door opened and it was 40°, that rule would become true.
Finally, you Actions for True, and Actions for False. When the rule is evaluated, it will be either true or false. If it becomes true, and it had been false, then the Actions for True are going to happen. If it gets evaluated to true, but it was already true before, nothing will happen. Same for false. For example, if the Door is closed, and temperature changes from 40° to 42°, the rule was false, and changing the temperature doesn't change anything -- it's still false, so nothing will happen.
You can read more about this here: Rule Machine® Introduction
