Applets are components that can be added in user interface to add functionnalities. Use the module tool in platform administration to install applets.
Tools that can be added to your courses. Use the module tool in platform administration to install modules. A course module is by default installed in all courses after you activate it but it remains invisible until the administrator or the course administration set it as visible.
Default Claroline editor is TinyMCE from Moxiecode. From Claroline 1.8 you can change the WYSIWYG editor used to edit rich text zones in Claroline. Unzip editors in the /claroline/editor/ folder of your Claroline 1.8.x.
Themes can be applied to change the look of your platform. Unzip themes in the css folder of Claroline and choose the correct css in the main configuration settings in the administration of your platform.
Icon sets replace the original icons of Claroline to change its look.