Receiving from external clients

Sorry if this is a basic question, but I haven’'t been able to resolve it on my own.

I am using Spark as a service of the university where I am a librarian. I have been able to chat with students at this university who logon to Spark and contact me using their university identities, but I’'d like to know how to allow myself to be contacted by students using Yahoo or AIM clients. Can someone please hold my hand and walk me through it? I can even see the Yahoo, AIM etc icons right there but I have been unable to figure out how to make it work. Thanks…