Shabbos question: Delayed actions?

I’m trying to understand the mechanisms behind shabbos laws. If I were to set a timer that would turn on a set of lights, and I set it before shabbos so that the lights would be triggered during, does this violate shabbos the same way it would to manually turn the lights on?

In the former case I am taking an action that will indirectly lead to a prohibited act.

If this is forbidden, would it also not be a violation of shabbos to purchase a product knowing it will be shipped on shabbos? In both cases you take an action that you know will lead to a violation. Though this case maybe illustrates a broader question I have about what qualifies as a violation. If one is prohibited from being in a vehicle on shabbos because it would consume fuel, wouldn’t something as simple as one’s body heat cause an air conditioner to use additional power?

Sorry if any of these are poor questions.