Tracking users– help! Does anyone know a good course on instrumentation?

...I don't really understand what Segment is. I've read the description, but I still can't tell if I need it.

For example, I want to know things like:

• when users log in and what they do within my app
• how long they spend on one page vs. another
• how often they open a modal

My previous apps are a mess of google analytics events that I can sort of (barely) make use of. Is that the best way to learn this info? Do I need Segment? Do I need Posthog?

Is there a good resource online that will teach me both the philosophy-behind and a strategy-to-implement instrumenting my apps to get the most useful user data (while respecting user's privacy obviously!)

As an aside, I have no idea if instrumentation is the right word. At one startup I worked at, that's what we called the process of making sure we had the right event tracking in place.

My question is does anyone know of any great resources online that helped make this click for them? I have a background as a developer so I'm not worried about integrations– it's really the thought-process and strategy that I'm hoping to improve in.

Thanks!