The main road: Tor Browser
The one download that opens every plate in this atlas.
Every address in this atlas is a Tor hidden service, and a hidden service only opens in the Tor Browser. This is the main road onto the map, and getting onto it correctly the first time closes most of the ways a crossing goes wrong.
Download from one place
The only source is torproject.org. Any other download page is either an unverifiable mirror or a modified build with something added that you do not want. If you land on a Tor Browser download that is not the official project site, close the tab and start again.
Check the signature the first time
The Tor Project signs every build. Verifying that signature against the project key is the difference between a clean browser and one that quietly leaks your traffic around Tor. The download page walks the check for every operating system. Do it once, on the first install.
Set the level to Safest
Open the shield beside the address bar and set the security level to Safest. That turns off scripting everywhere, which removes the most reliable path anyone has to break Tor's anonymity from inside the browser. The markets in this atlas are built to work at Safest, so you lose nothing you need.
Leave the window alone
Do not resize or maximise the window, and do not add extensions. Both make your browser fingerprint unique, which is the opposite of what Tor is for. The browser ships anonymous. Every change you make chips at that. Use it as it comes.
Once the road is open, the rest of the atlas is a matter of copying the right address and reading the terrain before you commit.