There are two general categories of bad actors that want to infringe on the privacy of the web: malicious governments with access to ISPs (Internet Service Providers) and mega corporations that run social and advertising networks. TOR (The Onion Router) is useful in protecting privacy from malicious governments but not from mega corporations.
Malicious governments often spy on their citizens to punish dissent or human rights activity. They commonly either operate the local ISPs or they can force them to disclose information showing every IP address that is visited by each user. Tor is designed to defeat this infringement of privacy by encrypting the traffic from a user's device and routing it through three separate servers on the internet before sending it on to the final destination. This means that no individual ISP, server, or website, can know both the IP address the user's device and the IP address of the final web server. Malicious governments and the ISPs they control cannot tell which web servers a user is accessing, although they can tell that the user is using Tor. In some parts of the world, using Tor could be construed as an evidence of illegal behavior ("if you didn't have anything to hide you wouldn't be hiding your traffic from us") and users could be punished because governments assume they are doing something that is prohibited. Thus, Tor can be helpful, but isn't a panacea.
They track every site that is visited, everything that is purchased, every credit card that is used to make a purchase, every address that items are shipped to, and the GPS metadata of every picture that is uploaded to the internet. They build a profile of a user's age, gender, marital status, address, political affiliations, religious affiliations, family circumstance, number of pets, and everything else they can get their hands on. They even buy up databases of credit card usage at local stores, so they can track the off-line purchasing patterns of the users in their profiles. Because they already have much more accurate address information about a user than an IP address discloses, Tor provides no real privacy protection against mega corporations.
Despite the limitations, Tor can be useful in some circumstances. The Tor project has an app for Android called Orbot, which is available on F-Droid and everywhere else that Privacy Browser is distributed. Privacy Browser has a setting to use Orbot as a proxy. When this is turned on, Privacy Browser's app bar will have a light blue background instead of the default light grey. When Privacy Browser's Orbot proxy setting is enabled, internet access will not work unless Orbot is running and connected to Tor. Because traffic is being routed through several Tor nodes, using Tor is often much slower than connecting straight to the internet.