Although Microsoft acquired Skype and incorporated it into their Office 365 suite, and since then into Windows 10, it is still possible to download it for Debian here: https://www.skype.com/en/get-skype/. However, it will only work if you have a 64-bit system.
If you’d prefer not to dabble with this installation you can use a great, yet very simple, alternative directly on the web. See Skype Alternative for more details.
If you’re continuing with the Skype download and installation, you need to choose the Linux DEB package (not Linux RPM or Linux SNAP) which will download skypeforlinux-64.deb into your Downloads folder.
Open a Terminal and change the directory to your Downloads folder:
cd Downloads
Then you need to find the file within your Terminal. You can do this by listing the contents of the directory in the order downloaded so that the skype file is at the bottom:
ls -ltr
Now to install it, you need to type:
sudo gdebi skypeforlinux-64.deb (you’ll be asked to enter your password before you can proceed).
You should now find Skype in your applications menu (Debian) or Internet menu (MX-Linux).