Thanks for your answer! I've read the content that you sent to me and I realized my web users should have their own account of Tableau Online or Server to access my dashboard. Do you know any way that EVERYONE can access my dashboard? (I kind of know it might impossible, but I hope somebody can find another way to display my dashboard)
If you post to public, everyone can access it. They only need accounts if you are posting to a private Tableau Server or to your account on Tableau Online.
+1 Agreed that publishing to Tableau Public Is your best bet, as you can EMBED once it is published to Public. Let us know if any questions. Happy analyzing with Tableau!
Here a good article with more information on publishing to public.
If the menu is disabled you may be on a worksheet or dashboards, maybe the data pane was active. Otherwise you should be able to publish the viz along with an extract of your data source.
If your student version is limited for some reason you could try Tableau Public Desktop.
If you don't have permission to publish a viz using this data then I may have misunderstood your original question because embedding in a public web page wouldn't be an option.