What do I not get about the rule machine?

[marktheknife]

Have you read through the hub documentation pages on rule machine?

https://docs.hubitat.com/index.php?title=Rule-4.0

https://docs.hubitat.com/index.php?title=Rule_Machine

As noted above, you initially added conditions but did not include them in the actions, hence your rule not performing as intended after the trigger occurred.

It looks like you've taken care of that part so far. To restrict your rule to occur only once after illuminance goes below your threshold (rather than every time the sensor reports illuminance below your threshold), you have a few options. Use of private boolean is probably a good one. You can find some more details on how to restrict actions in Rule 4.0 (the current version of Rule Machine) in this thread:

Rule 4.0: Retirement of Restrictions

Restrictions being Retired Rule 4.0 is no longer going to have a section to define Restrictions. Restrictions were specified conditions that would prevent a rule from running. These are being retired for two reasons: Restrictions are no longer needed, as all of the conditions can be incorporated directly in a rule. Restrictions introduce unneeded overhead for every rule, while most rules do not use them. Thus, by retiring them, all rules will become more efficient. Nothing is logged when a r…

Edit: also, you don't really need the illuminance conditional statement in the actions, because the rule is triggered by illuminance <150; in other words, that condition is already implied every time the rule runs.