To open a Mendix page from within a Mendix application, you don't need a “link” per se, you just need an “open page” action in your microflow, or a “show page” button. You can select the page you want to open in your “open page” action.
If you do need actual distinct URLs for some reason, you can fill them out in the page properties:
If you want to link to specific forms or microflows via a URL, you could consider using the Deeplink Module.