You can play with other people running Minecraft: Windows 10 Edition Beta who are on the same network as you are. You'll be able to play online with Xbox Live and with Pocket Edition (for iOS, Android, and Windows Phone) players after a future update.
An official server binary for PE/W10E is in the works.
When will the fix for external severs happen
It doesn't display a server once you have added it
But it wrights to servers.txt file
Hi,
There currently is no support for external servers in Minecraft: Windows 10 Edition.
As explained on https://support.xbox.com/en-US/xbox-on-windows/game-titles/minecraft-windows-10-edition-beta-faq:
An official server binary for PE/W10E is in the works.
Is "in the works" the best you can give us atm?, maybe in afew months, weeks, days?