There are a few different ways to restore your Launchpad on your Mac. The first way is to simply go into the System Preferences and click on the Reset button at the bottom of the Launchpad preferences pane. This will take you back to the default settings for Launchpad. If you want to be more selective about what gets reset, you can hold down the Option key while clicking the Reset button. This will give you a menu of different options to choose from, including resetting only your Dock or only your Dashboard.
If you want to completely remove all traces of your customizations and start from scratch, you can do so by deleting the com.apple.dockfixup.plist file from your home directory's Library/Preferences folder. Once this file has been deleted, relaunch Terminal (found in /Applications/Utilities) and type in defaults delete com.apple. This will remove all customizations made to Launchpad and return it back to its original state when first installed on your Mac.