Opening an Onion Link
An onion link is just an address that only the Tor Browser understands. If you paste it into Chrome or Safari it will not resolve, because those browsers do not speak the Tor protocol. Inside the Tor Browser it opens like any other site, and the whole task is a few seconds once you have the address in front of you.
Paste, do not type
Copy the address from a source you trust and paste it into the address bar. A fifty six character string is not something to retype, and a single wrong character is a different site. Pasting removes the typo risk entirely.
Wait for the circuit
The browser builds a path through the relays before the page loads. That takes a few seconds. If it stalls, the address may be under load or the circuit is bad. A new circuit, or the next mirror, usually fixes it.
Confirm you are on the onion
The onion icon in the address bar means you are on the hidden service, not a lookalike domain. If the icon is missing, you are not where you think you are. That one glance is the cheapest check in the whole process.