To install Cydia you have to jailbreak your iPhone/iPod Touch or iPad. There are lots of ways for you to jailbreak, depending on which device you possess and what version of iOS you have actually installed. Most especially, you can easily use blackra1n, redsn0w, PwnageTool, Spirit jailbreak, jailbreakme 2.0, as well as QuickPwn.
If you already have Installer. app on your device, you simply need to add http://apptapp.saurik.com/ as a source to Installer and install “Cydia” from the “System” classification. Generally if you upgrade your iOS to the latest variation from Apple, it will unjailbreak your device and you want be able to install Cydia anymore. Jailbreak designers typically support point’s one release behind the active iOS model. There are many ways to learn how to install Cydia relying on what iOS variation you have.