Every Drupal site I build involves at minimum two environments: one is on my laptop, which I call the local server; another is what most people call the production server. Drupal has a very straightforward way of allowing you the developer to use a single code base to run both environments, even though they are on different machines, in different corners of the world, with different passwords, etc.

A common development practice is to keep a local web server running on your laptop, or a development/staging server. A feature of Drupal designed for multisite installations can actually help you out in this situation.

Different servers often mean different databases, database users, and passwords. Sometimes, you may also need to point to a different files/ directory or tmp/ directory, especially if you are moving between Windows to Linux, or a local machine to a server.