Select a collaborative tool to work on the design of your site with your teammates. If you have doubts about which tools to use or what guidelines to follow for the visual design of a web application, see the article Fundamentals of Interface Design and User Experience - UI/UX
Build your designs on a platform that is collaborative and allows you to publish your work for anyone to see.
Once you have finished building your designs be sure to enable public visibility and attach the URL to your designs.