Sometimes you may only want your module to be loaded on certain conditions. For instance, mainpage loads on the home page but not when any other modules are run. However, the user module has to load no matter what other module is loaded. Check the radio button for 'All' if your module must always be loaded. Otherwise, click the 'Only' option then choose the other modules you want your module to initialize on. Your module will default to an 'On' position.