Single-letter options are convenient since they are quick to write and use, but as there are only a limited number of letters in the alphabet and there are many things to control, not all options are available like that. Long option names are therefore provided for those. Also, as a convenience and to allow scripts to become more readable, most short options have longer name aliases.
Long options are always written with two minuses (or dashes, whichever you prefer to call them) and then the name and you can only write one option name per double-minus. Asking for verbose mode using the long option format looks like:
curl --verbose http://example.com
and asking for HTTP redirects as well using the long format looks like:
curl --verbose --location http://example.com