The Cydia jailbreak app can be used by downloading the appropriate jailbreak software to your iOS device then tapping on the Cydia store icon. Cydia offers access to a huge number of third-party tweaks and apps not offered in the App Store.
To install both the jailbreak and Cydia, first determine which release of iOS is installed on your device. Then, download the appropriate jailbreak package from GuideMyJailbreak.com. Plug your device into your computer, and then open the jailbreak program. Follow the prompts to install Cydia, and restart the device.
Once the device has booted, tap on the Cydia store icon on the device's home screen. To use Cydia, find a tweak, application or theme you want to install in Cydia's store browser. Tap on the device to open the information screen. Then, click the "Install" button located on the top right hand side of the screen. This begins Cydia's installation process. Once the app has been installed, the user is often be prompted to reset their device. After the device reboots, the installed app is ready to go. Cydia apps can be installed in bundles, and it's often most efficient to download several apps at a time. To gain access to more apps, navigate to the settings page in Cydia, and open the Sources page. This is a list of all the websites Cydia is aggregating apps from. New websites (called repositories) can be added, vastly expanding the number of downloads available through Cydia.