In my experience online collaboration is working together with someone or as part of a team, but everything is done online! So you might use interactive word documents or powerpoint presentations (that everyone can edit at the same time), video conferencing, emails, that sort of thing!
The social network is basically any online website or app that allows people to connect and communicate socially! Ie Facebook, Instagram ect
Online Collaboration to me also means working as part of a team online using different computer programs like Microsoft Word and Powerpoint, Skype and E-mails. Online collaboration can also be done on social media platforms like Facebook! (Which brings me to your next question of Social Networking!)
Social Networking is when you talk to someone online! This can be done through websites/apps like Facebook, Instagram, Snapchat. Even Linked-In is an example of social networking for professionals and businesses.