VPNs (Virtual Private Networks) encrypt your traffic locally and send it to a VPN server. This stops your ISP or anyone monitoring the network from seeing your network traffic unless the VPN has been compromised. VPNs can be very important for privacy and security.
VPNs can also be very harmful for privacy and security. This is because a VPN provider may be logging all of your traffic and selling it. VPNs are also very vulnerable to traffic analysis attacks. These make de-anonyimizing a VPN user very easy. VPNs should not be used for anonymity. If you want a trustless, anonymous network, then use Tor or another anonymous network like I2P.
Choosing a VPN is mostly your preference but this will tell you the best ones, in my opinion.
The VPNs I would recommend are ProtonVPN, Mullvad and Windscribe.
NordVPN leaks your email to a tracking company and has trackers in their android app. As long as you don't use their android app and give them a fake email you should be fine.
Windscribe is based in Canada which is part of the 5 eyes. The devs do not think this is a problem as explained here.
Mullvad is based in Sweden which is part of the 14 eyes. I personally do not think this is that big of a deal as explained by the Windscribe devs.
A VPN called PIA has made a smear campaign about a few VPNs such as NordVPN, ProtonVPN and Cyberghost. They claimed that Nord and Proton both log and that they were owned by a company called Tesonet. This has been disproved and is a blatant lie by PIA to boost their own VPN. They also claimed that Cyberghost were based in a different country than they say. This has no evidence to back it up and going by what they said about Proton and Nord this is most likely part of the smear campaign.
If you want in-depth trusted, VPN reviews then you should watch Techlore on Youtube.