I just create a public webapp. However, I don't understand how I can share it with the other members of the organization. When a non-Dataiku user tries to access the url gets a blank page "This site can't be reached". Is it necessary to be a Dataiku user? From what I read in the documentation it shouldn't ("When a webapp is public, being an authenticated user is not necessary in order to access the webapp, and no authorization control is performed").
If that's the case, what are possible solutions to make it available outside DSS?
Indeed if you make a webapp public, users are no longer required to authenticate to DSS in order to view the webapp. However, users still must be able to load your DSS instance URL from wherever they are attempting to access the webapp. So for example, you could try accessing your public DSS URL from an incognito tab from a computer you usually use to access DSS, and you should be able to see the webapp without logging in.
From your description of the "This site cannot be reached" message, it sounds like there may be firewall settings that prevent the user from actually accessing the DSS instance itself. You can see if they are able to access the URL for DSS at all. If not, then you would need to work with your networking team to see if adjusting the firewall rules is an option.