Many smartphone, tablet, and game console makers include a layer of Digital Rights Management (DRM) software on their products. This DRM exists either to limit the software you can run on it, or is there for security reasons. Jailbreaking your iPhone means freeing it from the limitations imposed on it by your carrier, allowing you to run “unauthorized” software and to make other tweaks to your operating system.
More technically, jailbreaking can be thought of as the process of installing a modified set of kernel patches (the kernel being the supervisor of the operating system) that allow you to run unsigned code. It also gives you root-level access, which is otherwise unavailable. The term “root” comes from UNIX, where it is the superuser account that has unrestricted rights and permissions to all files. This provides you with added flexibility, but it also has some inherent dangers.
iOS is a closed environment: Apps need to adhere to Apple’s stringent guidelines to make it onto the App Store. To a certain extent, this restriction exists for your own protection and to maintain the overall quality of apps.
To Apple, an app is like a sandbox. Your app can only play within the sandbox, but if you want to roam outside of it, jailbreak iOS is your only option. It lets you do everything from customizing the look of your iPhone to installing third-party applications (such as titles that are not authorized and available in the App Store) and customized ringtones on it. Depending on how far you’re willing to go, you can do even more than that: Jailbreak iOS even lets you to unlock your phone so you can use it with a carrier other than the one from which you purchased it.
There’s a ton of third-party apps available once you jailbreak your phone. Some of them are really fun, some of them are really useful, and plenty of them are really cool. Sure, many of them are available in the App Store, but there are many, many more unauthorized apps that are also available
Jailbreaking iOS has some inherent risks. Once you do it, you’re on your own. You may have voided your warranty, so you can’t rely on your carrier or Apple to fix any problems you encounter.
For safety it is better to have professional expert to help you jailbreak your iDevice.