Well, you'll need to store the session data in a cookie. You can use
-c cookie_filename to create the cookie (add this to your login command). And then, for the other requests, you can read from the cookie with
curl -s loginpage -c cookiefile -d "user=myself&pass=secure"
curl -s secretpage -b cookiefile
Notice many times
loginpage is not the page you open with your web browser where you introduce your user and password. You'll have to check where the form is posting that data to (search the
<form> tag in the source code and the
action=... attribute). So, for example, if you want to log in to http://criticker.com,
loginpage is http://www.criticker.com/authenticate.php and not http://www.criticker.com/signin.php, which is the one you open with your browser.
If you use Firefox, a plugin like Tamper may help you find the correct
loginpage and all the data that is being posted to it (like hidden input fields in the form).