Good questions! The to-do list should live somewhere that all relevant stakeholders can see it and chime in. That's going to vary based on the team, project, and task, but in general, the more visibility the better.
A to-do should at least have a brief description of the task and some way of tracking who's working on it. As people discuss and begin work on the to-do, it can be helpful to add supporting links, screenshots, demo videos, etc. There are plenty of tools that do this well -- I've enjoyed working with Basecamp and Trello.
I wouldn't worry about trying to conform to any particular format, especially when you're just getting started. I think to-dos should be about getting context out of individual's brains into a shared space rather than adding unnecessary process or bureaucracy.
Teams that are working with Microsoft stack, often use VSTS to manage their backlog. 🙂
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