I am making regular updates to the online documentation at
https://projects.privateeyepi.com/home.php, all the latest updates are posted.
The work to show the new Desktop options from the old options is still a work in progress.
The GPIO option is generic, the Door option would be the right answer if the GPIO pin was being used to monitor a door.
The "decimal" is how many decimals do you want displayed 0, 1 or 2. Most temperature sensors provide 2, pressure sensors provide 3. User option.
The suffix is the letter behind the number, F for Fahrenheit and the system will put a temperature icon in front of the F, C is usually for Centigrade, L would usually be Lux/lumens .
The suffix is any letter that means something to you, the system does not care, it only displays it.
Glenn