These are passwords that users have to generate in order to start using 3rd party apps. Because Calbot is a 3rd party app to Apple - our users have to generate those passwords in order to connect their iCloud calendars to Calbot.
Apple gives a pretty detailed guide on them here.
Unfortunately, Apple made it this difficult and there is nothing we can do on our side to make the user experience better without compromising security.
To generate an App-Specific password for Calbot:
1. Go to the Apple ID page and sign in.
2. Go to the Security section, find App-Specific Passwords section and click on Generate Password.
Please make sure you have 2 Factor Authentication enabled! Otherwise Apple won't let you generate an app-specific password.
3. Name your password whatever you want (preferably Calbot, so that you know what it is).
4. Copy and paste the password Apple has generated into the Calbot iCloud Calendar connection window and click proceed.
Luckily, you only have to do this process once, but we are sorry for the pain :(