Stick with the sources that Cydia provides, until you are really comfortable with Cydia tweaks and apps. Cydia has several sources like the BigBoss repository and they are safe and you should pay attention to the specs for an app before you download it, and be sure it supports your version of iOS. Try to download only one app at a time, check it out and be sure there's no problems before downloading the next app. This will make trouble shooting much easier, in case you run into an app that conflicts with another app. If your having trouble with a new Cydia or Apple app, try a hard reset, Close all apps then - Hold down the HOME, bottom button, and the SLEEP, top button, for about 10 seconds until the Apple icon appears, then release buttons. Allow it to reboot, it may take a few minutes, don't panic like I did, wait for it to reboot. Cures many weird problems on iOS devices.