Thunderbird is a email client. The Linux Mint Cinnamon is a Linux distro where the desktop environment is Cinnamom as there is also Xfce and Mate options. To download the Linux Mint iso go to https://linuxmint.com/download.php and https://linuxmint-installation-guide.readthedocs.io/en/latest/ will help go about the basics of the installing. If you are interested in installing Linux Mint either as a dual boot with your Windows install or to replace your Windows install then you may get more help at https://forums.linuxmint.com/ forum.