A Facebook web app at its simplest is an html page hosted on Facebook. Build your Unity app for the web and then deploy it as a Facebook app.
Here is the basic process:
Create Unity application.
Build a web build. This will generate an html file and a unity3d file. (Note that the html file can be modified to suit your needs, just make sure it loads the Unity build. And of course your users will need the Unity web player plugin installed.)
Host the html and the unity3d file on your web server.
Enter your application information, making sure to set the “Canvas URL” to link to the Unity html file posted in step 3.
There are lots of details I haven’t covered, but that should get you started. There is lots of info over at developers.facebook.com.
If you want to communicate between the Unity app and Facebook, the Graph API is the usual way to do so. You can use this from client-side javascript embedded in the html page that also launches your Unity game, or you could use it from within Unity itself via the WWW class. The latter approach requires jumping through some hoops (security, web request/response, etc.) and may be simplified by using a third party Unity add-in for Facebook communication. If you search the asset store for “facebook” there are lots of resources. I expect the better of these also provide information on Facebook publishing.
Thx for your help but I have a problem with the Facebook Canvas URL.
I hosted my game in WebGL in a public folder in GoogleDrive, the game is loading and is working very well when I’m testing it with my browsers (so the hosting is working…).
But in the Facebook Canvas URL, they say : This URL must end with a “/” or have a “?” in the path