1. Download Tor Browser from the real source
Open torproject.org or its onion at 2gzyxa5ihm7nsggfxnu52rck2vv4rvmdlkiu3zzui5du4xyclen53wid.onion. Do not use a random mirror. Do not use the Chrome Web Store copy called "Tor". Pick the build for your OS and verify the signature once for good measure.
2. Set the security slider to Safest
Click the shield icon next to the address bar, choose Change, pick Safest. This disables JavaScript everywhere. Nexus works fine without JS because the login flow is old-school HTML forms.
3. Copy a Nexus URL from a source you trust
The primary onion is on our home page. Backup mirror links are on the mirrors page. Copy any of them. Do not follow a link that was posted in a random forum thread and do not click a Nexus link inside a search-engine advert.
4. Paste and wait through the queue
Paste the URL into Tor Browser's address bar and press enter. The first screen you see is the anti-DDoS queue. It shows a rolling counter and a rough position. Wait. This is Nexus verifying your Tor circuit before it lets you touch the login form.
Queue times swing widely with load. Ten seconds on a quiet day. A couple of minutes during a spike. If the queue clears instantly on every attempt from the same mirror, the mirror is fake.
5. Solve the captcha and read what is inside it
The captcha image at the login screen prints the current onion URL along its bottom. Solve the puzzle to prove you are human. While the image is visible, glance at the URL under it. It should match the URL in your address bar exactly. If it does not, close the tab. You are on a phishing mirror.
6. Log in or register
Registration on Nexus is free and asks for nothing more than a username, a password, and a mnemonic PIN for account recovery. Copy the mnemonic to paper. Do not screenshot it. Do not save it in a password manager that syncs to a cloud service.
What to do if the queue is stuck
Close the tab, right-click the toolbar, pick New Identity. This gives Tor Browser a new circuit and starts a clean session. Paste the URL again. If the queue still stalls, try a different mirror URL from the mirror list. Different mirrors sit behind different Tor introduction points, so an attack that pins one will often miss the next.