Easy answer for most installations:
- If database and URL remains the same, you can move by just copying your files and database.
- If database name or user changes, edit wp-config.php to have the correct values.
- If you want to test before you switch, you must temporarily change “siteurl” and “home” in the database table “wp_options” (through phpMyAdmin or similar).
If you had any kind of rewrites (permalinks) setup you must disable .htaccess and reconfigure permalinks when it goes live.