The information you've received sounds a lot like how to adjust an existing topic. For that, you need to be granted topic admin privileges by one that already has those privileges for that topic. That's not relevant for your purpose here, though.
What you'll need is the guild notifier privilege. To find out if you have it, go to "Create Message". If you have the privilege, the button "Add All Guild Members" will be prominently visible here; you simply can't miss it. If the button is there, before you go ahead, consider that the fastest way to loose a privilege is to abuse it, and that your guild's leaders will probably appreciate it if you inform them before creating the topic, and then make them co-admins of the topic once you've created it (which you do via the little blue button at the top left of the topic).
If you don't have notifier privileges, that will be deliberate, and means that they don't want just anyone creating topics. Your realistic option will then be to send them a suggestion for the creation of the topic. It's a very sensible suggestion, by the way.
First thing last: If you're very new to the guild, there's a chance that the topic already exists, but you haven't been added to it yet. It's sloppy, but it happens.
