This is the main window. It’s where your contacts are listed–so it functions as the hub of all of your Skype for Business activities.
If you click the IM button , you’ll get the conversation window.
Tip: You can also just double-click a contact’s picture to open the conversation window and start an IM.
This is the conversation (IM) window.
Click the happy face to add emoticons to your IM.
And this is the meeting window