Initiate or receive from a PC

Hello, I got Chalk installed on my iphone and got several colleagues invited. They activated their accounts. What else we have to do to start the call? I assume they can also install the chalk on their phone and then we can call each other. Is there a way to us PC? for remote assistance, one of the caller should be in office and have a PC. it is much easier than using phones. But I could not instructions on installing/using chalk on PC??? Thanks!