What is the best way to add Facebook Connect, Google login, Linkedin login, etc to my website?
If you have programming skills there are developer communities for each that provide how to guides on how to implement this feature into your website. Links provided below:
https://developers.facebook.com/
https://developers.google.com/accounts/
https://developer.linkedin.com/apis
If you have a wordpress or similar product there are many plug-ins that are available to accomplish this here are three links below to a plugin for each one.
https://wordpress.org/plugins/linkedin-login/
https://wordpress.org/plugins/tags/facebook-login
https://wordpress.org/plugins/google-apps-login/
Otherwise, you really need to hire someone with programming skills that can assist with this. You can find programmers on many sites like Odesk, Elance, freelancer.com or similar sites.
I have included links above for each developer community, as well as, WordPress plug-in links, but apparently they will not become visible until I receive 5 votes as I am a new member here. But the links can easily be located doing a search in your favorite search engine.