Tor: How do I download Tor Browser safely?

Short answer

Start at the Tor Project's official download page rather than an advertisement, mirror you found at random, or an unofficial app store listing. The Project also documents GetTor and official mirrors for places where its website is blocked. Choose the package for your operating system, and verify the accompanying signature if you need confidence that the file was not altered.

Sources

Tor Project: Downloading, Tor Project: Verify the signature.