From nothing to the storefront in four steps.
Four things stand between a clean machine and a working Anubis session, and the order they happen in is not negotiable.
An ordinary browser cannot resolve an onion address at all, so this is not optional. Take it from the Tor Project itself, typing the address rather than searching, because paid results for browser downloads are a known distribution route for altered builds. An altered build behaves normally right up until it does not, and nothing visible distinguishes the two.
A signature file sits next to each release. Checking it proves the bytes you have match the bytes published, which is the only claim about the file you can actually establish. Ten minutes, once, and the warning about the key not being certified is normal rather than a failure.
The bundle arrives on its most permissive setting. Safest disables scripting everywhere, which closes the route most browser compromises have taken for a decade. Pages become plainer. That is the setting operating correctly, not a problem to work around by turning it back down.
This market takes four, which means the payment decision arrives earlier than you expect. Acquiring the one you actually want is slower than every other step here, so deciding at the checkout screen means paying with whatever happened to be lying around. Read the comparison before you buy anything.
Copy rather than type. Wait for the page without cancelling, because tens of seconds is normal for a first connection. At the login screen, compare the printed onion against your bar reading right to left, and continue only on an exact match.
The opening request builds everything from nothing. Once it is up, the rest of the visit runs at a completely different pace, which is why doing everything in one sitting beats returning three times.