If you want to start a meeting right away rather then schedule one in advance, you can use instant meetings or call another user directly from chat.
To start an instant meeting
Choose Meetings, Start an Instant Meeting.
Choose Personal or One-time Meeting ID.
Choose Mic & Speakers or Dial-in.
Add the users to invite to your call.
To start a call from chat
Choose the phone icon in the top-right corner of the screen.
The call starts with all the chat users immediately.