Open a .onion the right way
A .onion is not a website. It is a service that exists inside a network, and a regular browser cannot see it at all. It needs Tor Browser. The setup takes about ten minutes, and it is done once, not on every visit.
Get the browser
Download Tor Browser from torproject.org only. That is the one source. Next to the download there is a SHA256 checksum, and it is worth spending thirty seconds on it, because a browser you loaded from somewhere else is the one place a mistake is expensive.
sha256sum tor-browser-*.Linux_x86_64.tar.gzRun that in the folder you downloaded to and compare the output to the sum on the site. They should match character for character. The bundle is small and the install does not drag in anything else, no toolbars, no "also install this" checkboxes.
On a phone the same rule holds. Onion Browser on iOS and Tor Browser on Android, both from their official sources. A .onion opened in anything else is not opened in Tor at all.
Settings before the first onion
There is a security slider in the browser settings. Set it to Safest before the first visit. Safest turns off third party scripts, web fonts, and media. Most of the market's pages are static, so the difference is small, but the safety margin is real. If a particular step does not load at Safest, drop it to Standard for that moment and put it back. Do not leave it down out of habit.
Do not add extensions unless they are the official ones. A random add-on that runs inside the same profile can undo what the network is trying to hide. And do not use the profile you use for personal browsing. Keep the market in its own window, so its history and stored logins stay separate from everything else you do on the machine.
The order of layers
Tor comes first. A VPN on top of Tor is optional. It hides from your provider that you are using Tor, which is useful on a network that marks Tor traffic. A VPN in place of Tor does not work for a .onion at all, because the address only resolves inside the Tor network. The short version: a clearnet VPN is optional, Tor is not.
The first test
Open one of the three addresses from the links page. If the screen "Checking your browser before accessing Nexus Market" appears, the routing is working and the rest is up to the market. If Tor will not connect to anything, not even to plain sites, the problem is your connection, not the address. That is the next section.
Blocked networks
Some networks block Tor outright. The fix is a bridge. In Tor Browser go to Configure, then Network Settings, then "Use a bridge". You will need a bridge string, which is requested at bridges.torproject.org. Paste the string in and reconnect.
There is a quick way to tell whether the block is local. Open the same browser on a phone hotspot. If Tor connects through the hotspot but not through your home or office network, the network is the problem, and the bridge is the workaround. If it fails in both places, look at the browser setup before you assume the network is at fault.