LinkedIn, to stay with the example, is going to give you a certain set of tools. How you use those tools is going to depend on your strategy. What that strategy is is going to depend on goals.
If you haven't or can't articulate your goals, you have to start there. Once you know what exactly it is you are trying to achieve, you can evaluate different strategies on how to achieve them (here it helps to also have a good idea of timelines or other constraints too).
So you have a goal (say, double engagement* with mid-career engineers in the next 12 mo), and a strategy (direct communication with targeted individuals, tailored by demographic), you can evaluate a tactic (post LinkedIn adds) and understand how it fits into your strategy based on the tools they give you.
* or some other metric, better if less handwavy
A LinkedIn ad (or a Facebook ad, microsite, TikTok, Snapchat), targeted at a specific audience or audience subset, might be one tactic amongst many that you used to drive people toward achieving this goal. You would have different tactics for different parts of the funnel (i.e. an ebook for someone at the top, and a demo or webinar for someone at the bottom). You would then measure the success of these tactics to determine where to direct spend to achieve your goal.
Trying to get sign ups? Track landing page conversions, forms filled, optimise, rinse and repeat.