Cydia comes with jailbreak, jailbreak is simply freeing yourself from the restrictions by the manufacturer, in this cas Apple. A jailbreak is available for different iOS versions, basically, if you have an iPhone 7 on iOS 10.3.3, you'll need a jailbreak that is compatible for that version. There are also jailbreaks for 32-bit and 64-bit devices.
To jailbreak, you need to to go in your settings and look for your iOS version, for example, if it's 10.3.3, you'll look for "iOS 10.3.3 for 64-bit device" since you have an iPhone 7.
And you'll just have to follow some steps.