I was about to discuss the proposal at https://area51.stackexchange.com/proposals/121892/operations-research-and-analytics and then saw that discussing a proposal is done in the form of ask a question on Area 51 Discussion Zone. What is the basic guideline for the proper way to edit the text in the title and body of the question after clicking "discuss this proposal?" I mean the rule I suspect almost everyone who has discussed proposals before knows. I don't know how it's supposed to be done because I'm probably supposed to insert some text of my own as well. The rule is probably something that will end up ensuring that the question refers to the right proposal. After I learn that, the other part of how to make the question end up being a decent enough question, I can probably judge on my own how to do.
The Discussion Zone is, as you've already figured out, the place for discussing proposals. There are a lot of things you can discuss, but here are some of the most common topics:
Proposal scope (is X on-topic for proposal Y?)
Name changes (should we change the name of proposal X to Y?)
Differences between a proposal and another proposal/site (would proposal X overlap Y too much?)
Writing a good question is fairly simple. Click the "discuss this proposal" button, then write what you want to discuss and all relevant details pertaining to the question. Other users can then vote on it (voting on meta is generally based on agreement or disagreement with the question), comment, and answer until a conclusion is reached.
I would personally recommend browsing around the discussion zone for a little while to see some examples of what makes a good question on meta. Everyone's first few questions on meta sites tend to be a little rough; stick with it until you start to understand how this place works.
Edit to address comments: When you click "discuss this proposal", you are creating a question about the proposal you're choosing to discuss. The default text signals to future viewers of the question that the question is discussion the proposal; unless you have a good reason to, please don't change the default text.
The title should summarize what you want to discuss. Describe the basic point of it; don't go into too much detail but make it stand out from other questions. This can be hard to do on meta sites, but it's definitely doable. See also: How do I write a good title?
If you are just trying to figure out the mechanics of how to ask a question about the proposed OR & Analytics site, you already figured it out -- your question was submitted the right way. If you're trying to propose a sample question, then use the box that says "Propose an example question" and then click the "Post Your Example Question" button.