what does curl represent code example

Example 1: curl return code only

curl -s -o /dev/null -w "%{http_code}" http://www.example.org/

Example 2: curl post request

curl -d "user=user1&pass=abcd" -X POST https://example.com/login

Example 3: curl get example

curl -i -H "Accept: application/json" -H "Content-Type: application/json" -X GET http://hostname/resource