When you sign up for webhosting, you usually get access to what is known as the "control panel" to your webhosting account.
Access to control panel enables you to setup email addresses, password protect directories, set up FTP accounts, create databases, check server logs, backup, and a whole lot more. Basically, it is the "one-stop shop" for all your administrative tasks. Many shared webhost's control panel uses a software known as cPanel. If your webhost uses cPanel 11, you can read the documentation to learn more.
Different webhosts will will have different ways of accessing your control panel.
1. Appending cpanel at end of domain name
For hostmonter, for example, it is accessed by going to http://www.example.com/cpanel where "example.com" is replaced by your actual domain name. It will ask for your usename and password.
2. Webhost home page
Other web host, such as bluehost, may have a "control panel" login box on their homepage where you enter your domain name and then your password.
3. Central Control Panel Login
Dreamhost has a central web panel login page. Dreamhost likes to be different and calls it a "web panel" instead.
If you are typing in the control panel password on a login page with and URL that starts with "http://", then your password is transmitted to the server in clear text. Ideally it would be better to transmit the password over encrypted channels via the "https://" protocol. See why you should use HTTPS over HTTP. Many good webhosts will provide a way to access your control panel securely via the "https" protocol.
For example, you will note that the Dreamhost central web panel login page URL starts with "https://".
Hostmonter provides an alternate way of accessing control panel by https://www.example.com/securecontrolpanel (where "example.com" is replaced by your domain name).