When you run a Google search, use Facebook, or go shopping online, your search data is being tracked, stored, and sold to third parties. This information is often used to send you targeted ads, which is annoying but not particularly dangerous. But sometimes collected information can make its way into unscrupulous hands. Hackers may access this data for identity theft, or the information may be used without your knowledge.
If a website (such as Facebook or Google) is going to sell your information to third parties, they often tell you so in the Terms of Service that you agree to before you use them. However, these documents are often long and difficult to understand. The Terms of Service; Didn't Read browser extension gives you a short summary of the terms, so you can figure out quickly what the site is doing with your data.
DuckDuckGo is a search engine (like Google) that doesn't track your activity as you use it (unlike Google).
Tor is a browser (like Firefox or Chrome) that has many security and privacy features built in, and allows more anonymity than other browsers.