Any iPhone models can successfully get the Cydia installer by using the jailbreak wizard. Jailbreaking is the only possible way to download Cydia for any iOS device. Cydia installs jailbreak software & methods varying from iOS version to version. For example- for iOS 5.1.1 (All) Absinthe 2.0 (untethered) is the perfect solution, for iOS 5.1 (A4 only), redsn0w 0.9.10b6 (semi-tethered) is the best.
Cydia is a replacement of the original Apple Installer app. With Cydia, you can search for apps by name, installed apps and upgrade. How to Jailbreak iOS 10 on iPhone