Add a contact in Skype for Business
IMPORTANT: You can't use Skype for Business on Mac to communicate with people who are using the free Skype app. You can only use it to find and communicate with people in your organization who are using Skype for Business.
Find a contact in your organization
Go to the Contacts list.
In the Search for Contacts box, type a name, email address, or desk phone number if they are in your organization.
If your organization uses Office 365 Groups, you can also search for the group name. As you type, search results will start appearing below the search box.
When you see the listing for the person IM or call, double-click their picture or picture display area.
Choose how you want to contact the person: IM, video call, phone call, email, or schedule a meeting.