Command line options pass on information to curl about how you want it to behave. Like you can ask curl to switch on verbose mode with the -v option:
curl -v http://example.com
-v is here used as a "short option". You write those with the minus symbol and a single letter immediately following it. Many options are just switches that switch something on or change something between two known states. They can be used with just that option name. You can then also combine several single-letter options after the minus. To ask for both verbose mode and that curl follows HTTP redirects:
curl -vL http://example.com
The command-line parser in curl always parses the entire line and you can put the options anywhere you like; they can also appear after the URL:
curl http://example.com -Lv
and the two separate short options can of course also be specified separately, like:
curl -v -L http://example.com