Questions about apps vs websites, cookies, tracking, etc [View all]

I am trying to understand the current state of tracking tech, and would like a more thorough understanding than just the basic stuff.

For example, the actual difference between using a website vs an app. How much actual info can an app take from your phone? It used to be that you could deny certain rights within apps that didn't seem appropriate (eg, why an app needs access to my mic or camera when I have no intention of using the app that way) and so on. I've always been on the cautious side, and lately I'm just getting fed up with all the stuff that corps are getting away with, and I want to make it as hard for them as possible. What prompted this was a Nextdoor (which I access via website, not app!) discussion about grocery store apps and digital coupons, something I don't use so miss out on a lot of deals.

First question is very basic: what info can a cookie contain? Is there a way to view a cookie file to see what it is collecting? I should mention my main tool is a smartphone, not a computer, so Android based.

Another recent event contributed to this concern: I recently used the Walmart (I know, don't start) website to order some items for shipping, to see how they compare to Amazon. What shocked me was that when I looked in the "prior purchases" section, it had items from years ago that were purchased in a brick and mortor store! Now, Walmart isn't like Costco, so the *only* way they could correlate that data is by using my credit card info!! Is this legal?? It really is bothering me.

Any sites that contain good info or discussions along these lines? TIA