Authorized redirect URI - What the heck is it?

I am trying to use the Socialink plugin in order to allow folks on my Wordpress site where most of the website content is located to use their Wordpress user account to login on my Elgg site. I installed and activated the Oauth plug in on my Wordpress site and got a consumer and secret key. In the setup in the Oauth plugin it asks for the "*Authorized Redirect URI :" I honestly have no idea what I should put there. I have put my main domain address (  and I get a 'page not found' when the login with wordpress option is taken. I have put in the home page of my elgg site (https://homegardenbook/elgg2/) and same think. I don't know what is the 'Authorized Redirect URI' nor where to find it. 

Can you please help me

Ron Tucker