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There are a couple of different ways to get an impromptu meeting going with just a few clicks.
From
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Your Calendar
Go to Calendar
on the left side of Teams, then select Meet now 
in the upper right corner.You'll have a chance to set a few things up before you start your meeting. Give it a title, choose whether you want to use video, and pick your preferred audio source.
When you're ready, hit Join now.
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Start typing the name or phone number of someone you want to invite in the box under People in the top right. Select them when they appear in the list, and they'll get a call right away.
Another option is to copy the meeting link and send it to anyone you want to meet with, and they can join by selecting it. Just choose Copy join info and paste the link in a message.
From a
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Channel
To get a channel meeting going right away:
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