Before you can do anything at all, you must have connected to the server of the site that runs Joomla.
Development of websites is often done on a local server, i.e. a virtual machine made out of software put on your computer itself. When operating on a local (virtual) server it is necessary to first start up the server. This is done in various ways, depending upon which local server environment you have installed. E.g. if you have installed XAMPP for Windows, you must first look up the 'xampp-control.exe' file and double-click it. A window called XAMPP Control Panel Application appears. Then you have to click the start-button next to the words "Apache" and "MySQL" otherwise nothing will happen. Green bars with the word 'running' should appear next to the words Apache and MySQL. This done, type "http://localhost/yourjoomladir/administrator" in the web address field of your webbrowser in order to attain to the login screen for Administrators of Joomla. ("yourjoomladir" is the name you have given to the directory where you installed Joomla 1.5.x on your local server.
The Administrator back-end of your Joomla! installation is where you do most of the work to set up, configure and maintain your website. As such it must be protected from access by casual visitors and so Joomla! will request a valid username and password before access to the Administrator is granted.
You access the Administrator back-end of your website by entering a special URL into the address bar of your web browser. If your website URL is http://www.example.com then you will enter the address http://www.example.com/administrator. You will be shown the Administrator login form which looks like this:
Enter your username and password into the relevant fields. If required, select your preferred language from the drop-down list. Then click the Login button. If you are logged in successfully you should see the Administrator control panel screen which looks similar to this:
To log out of the Administrator back-end, locate the Logout link in the top-right corner of the Administrator screens and click on it. Logging out will return you to the Administrator login screen. If the Logout link is greyed out and nothing happens when you click on it, then you are probably in a screen where you have some resource locked for your exclusive use. Click the Cancel toolbar button first to release the resource, then click on the Logout link.