The packages comes with a post-install script (that is, literally a script that is executed after the package has been installed), which automatically downloads the fonts from Microsoft.
They should already be installed on your system, right after you have Accepted the end-user license agreement.
You can find the fonts in
/usr/share/fonts/truetype/msttcorefonts/. You may (I'm really not sure) need to refresh the font-cache so that applications can use them, or maybe the script has done that for you. The easiest way to make sure everything is up to date is to reboot your computer.
If the folder /usr/share/fonts/truetype/msttcorefonts/ is empty try to use the command
sudo apt-get install --reinstall ttf-mscorefonts-installer and agree the license