Unfortunately, I'm not trying to be funny. It is appalling how resistant many members of this group are to doing web searches for simple questions. And posting the same question, twice, in less than 2 days when the first had no takers does not endear one to the readership. If someone knows, they'll answer the first time asked.
Anyone who wants to know more about the "Meet Now" feature, which includes its button, should choose the web search engine of their choosing and put in the following short set of search terms:
Windows 10 +"meet now"
When something is this new there are going to be very few end users who can answer anything about it, as it just came out. I'm among those who know this feature strictly on the basis of what Joseph Lee had posted in a recent cumulative update announcement. Those who have been running insider builds and the tech press are generally where one gets the best information on a brand, spankin' new feature.
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
If your joy is derived from what society thinks of you, you're always going to be disappointed.