On the main screen of your administration system you will see a button that says Add New Article

Click this button and you will see a new content editing window.

Please make sure you select a Section and a Category that this page will be stored under. Now write some information in the Intro Text window. Once you are finished typing your info click the Save button at the top right of the screen.

Please note: new content pages will not automatically appear on your site until you create a menu link to it. The howto called "Add a content page to your menu" will help you do this.