You can make one-on-one or group calls with anyone in your organization directly from a chat without having to host a team meeting. These calls are private and won't appear in any team conversation. Entries for the calls will appear in your chat, though.
Go to your chat list, and click New chat
to start a new conversation.Type the name or names into the To field at the top of your new chat.
Select Video call
or Audio call 
to start a call.
Up to 20 people can be on the same video call.
Note: If a group chat includes more than 20 people, calling buttons will be disabled.
If you're not currently in a chat with the person you want to call, you can start a new call from a command. Go to the command box at the top of your screen and type /call, then type or select the name of the person you want to reach.
You can also start a one-on-one call from someone's profile card. Open it by clicking their picture in a channel or from a search.