Best use-case for vpns [free plan]

I think PrivacyGuides’s guides on the topic are quite exhaustive and cover all the topics mentioned (VPNs, DNSes, etc).

Privacy Guides

How Do VPNs Protect Your Privacy? Our VPN Overview - Privacy Guides

Virtual Private Networks shift risk away from your ISP to a third-party you trust. You should keep these things in mind.

There is a lot to read but everything said there will only be said in a less complete manner here on the forum so start reading there and ask precisions on particular points if needed.