General code-completion settings can be edited in the "Completion" pref pane, as described below. Language-specific code-completion settings are edited in the "Languages" pref pane.
If enabled, skEdit will bring up the code-completion list automatically as you type. Otherwise, you will need to hit F5 to bring up the list. This setting can be set independently for element-based languages, such as HTML or ColdFusion, and other languages, such as PHP.
If enabled, skEdit will index your files using the definitions provided by the appropriate bundle. Symbols found (such as functions, classes, etc.) will then be presented in the code-completion list when appropriate. More info.
The Code-Completion Preference Pane