The installation folder is where theBat is installed, typically
"C:\Program Files\The Bat!\"
(If not there and you can't find, search your disk for thebat.exe - the folder where thebat.exe resides is the installation folder).
In WindowsExplorer right-click the installation folder and sel ect 'Add to archive', 'Add to zip', 'Add to zip folder' or something alike, depends on what archiver (WinZip, WinRar etc.) you have installed.
If you do not have any archiver, simply copy the installation folder to another place to have a backup.
A backup of the installation folder is needed if after the upgrade the new version does not behave correctly, in such case you may want to revert to the older version.
Which is the mail folder you can see fr om theBat, click
Options / Prefernces -> System and see 'Mail directory'
Backup the mail folder as explained above. It's recommended to use an archiver to reduce the size of the backup. As the mail folder keeps everything important (emails, filters, address books etc.) , it's recommended to backup this folder regularly.
Before making backups, make sure theBat is closed.