What is Cydia?
Cydia is a software installer that helps you exercise the freedom of your jailbroken device — letting you install any kind of software you want, and helping you make your device even more useful and fun by customizing it to look and work the way you like it.
Most of the packages available through Cydia are not exactly "apps". Instead, they are a more flexible kind of software: tweaks (extensions and modifications) and themes for your existing apps, or for the whole experience of using your device.
Cydia includes access to lots of free and paid software and themes by developers and designers from the jailbroken iOS community, and Cydia's decentralized structure means that anyone can also use it to distribute their own packages.
I installed something, but there is no app icon for it. Where is it?
Most packages available through Cydia do not have app icons. Instead, they are customizations and extensions for other apps, or for parts of the interface of your device.
Check the package's description page to find out how to use that package. Many packages also let you configure them in your device's Settings app.
How do I uninstall Cydia packages?
Tap Installed, scroll to the package name, tap it, tap the Modify button in the upper right corner, tap Remove, tap Confirm.
Can I filter Changes to only show my favorite types of packages?
Yes! Tap Sources, tap All Sources, tap Edit (in the upper right corner), and turn off any types of packages you are not interested in seeing in Changes.
All types of packages will still show up when searching for package names.
To find out the section (category) of any package, visit its description page and scroll to the bottom.
If I get a new device, can I reinstall products I have purchased?
Yes, you can reinstall your purchased products on new or restored devices (if they are jailbroken). On Cydia's homepage, go to Manage Account and log in with the account you used when previously purchasing those products (a Google or Facebook account), and then tap on Installable Purchases to install them.
Make sure to use the same account you used before. If your purchases do not show up, try logging in with another Google or Facebook account. Try all possible accounts.
(If you have updated your Facebook or Google account email address, make sure to use your account's current email address and password to log into your Facebook or Google account, not any old ones.)
Can I buy products without having a credit or debit card?
If you have some cash but no credit or debit card, you can buy a prepaid general-purpose gift card and link it to your PayPal or Amazon Payments account. Then use your PayPal or Amazon Payments account to purchase products in Cydia.
You can often buy this kind of prepaid card at convenience stores, such as at 7-11 stores in the US. For example, Vanilla Visa is a popular brand of prepaid gift card in the US.
PayPal details: PayPal options for prepaid cards also include MoneyPak cards. Alternatively you can add funds by linking your bank account to your PayPal account.
Amazon Payments details: Similarly, you can add funds to your Amazon Payments account using a prepaid card or by linking your bank account to your Amazon Payments account.
Note that Amazon.com gift cards do not work for buying Cydia Store products — those gift cards are only good for buying products on Amazon.com itself, not for buying products on other websites that use the Amazon Payments service.