There are 3 ways to make a call:
Method 1: Open Teams and click on the Calls tab. Type a name or number into the field at the top and click the Call button.
Method 2: Open Teams and click on the Chat tab. Click the New Chat button, enter someone’s name, then click the Call button.
Method 3: From any place in Teams, click someone’s icon (usually their initials inside a colored circle) and click the Call button.