Tor is a software project that lets you anonymously browse the Internet. Tor2web is a project to let Internet users access Tor Onion Services without using Tor Browser.
Whenever you see a URL like http://duskgytldkxiuqc6.onion/, that's a Tor Onion service. Just replace .onion with .onion.to or .onion.city or .onion.cab or .onion.direct or any other domain made available by volounteers Tor2web operators Example:
https://duskgytldkxiuqc6.onion.to/
This connects you with Tor2web, which then talks to the onion service via Tor and relays the response back to you.
WARNING: Tor2web only protects publishers, not readers. As a reader installing Tor Browser will give you much greater anonymity, confidentiality, and authentication than using Tor2web. Using Tor2web trades off security for convenience and usability.