Usually it is https://youtube.com/user/CHANNELNAME or https://youtube.com/channel/CHANNELID
A good example is https://youtube.com/user/Google
Now go to your dashboard and manage your website(s) and check how many activities (e.g. tweet, like, share, etc.) you've got.
Important Note: It may take hours to get activities. So keep coming back to your dashboard to check what did you get.