Make sure that you've read the configuration wiki page first.
Amfora allows you to set the command to be run when following links that are non-Gemini URLs. For example, you may want mailto: links to be opened with your email client, or magnet: links to be opened with your torrent software.
[url-handlers]
# Allows setting the commands to run for various URL schemes.
# E.g. to open FTP URLs with FileZilla set the following key:
# ftp = ['filezilla']
# You can set any scheme to 'off' or '' to disable handling it, or
# just leave the key unset.
#
# DO NOT use this for setting the HTTP command.
# Use the http setting in the "a-general" section above.
#
# NOTE: These settings are overrided by the ones in the proxies section.
#
# The best way to define a command is using a string array.
# Examples:
# magnet = ['transmission']
# foo = ['custom-browser', '--flag', '--option=2']
# tel = ['/path/with spaces/in it/telephone']
#
# Note the use of single quotes, so that backslashes will not be escaped.
# Using just a string will also work, but it is deprecated, and will degrade if
# you use paths with spaces.
# This is a special key that defines the handler for all URL schemes for which
# no handler is defined.
# It uses the special value 'default', which will try and use the default
# application on your computer for opening this kind of URI.
other = 'default'
As mentioned above, the settings in this section are overridden by the ones in the [proxies] section. More information regarding this can be found in the proxying wiki page.