smart contract auditing journey

First of all - you'll need smart contract development experience. Audits can't be fully automated and the best way to understand potential problems is to deal with them yourself. Then I'd suggest checking out some courses targeted at audits like this one - https://github.com/Cyfrin/security-and-auditing-full-course-s23 (you can easily find more of them in google)

Once you have some hands on experience you can check open source contracts and try to find problems in them. It will be hard to find problems in most popular ones like USDT since it was audited many times already, but for less known projects you can actually provide help while gaining experience