StopCopy helps you protect your personal data in your clipboard. Some applications, when you open them, paste your clipboard data, you can see that because there is a warning appearing when that happens on the top of your screen stating: [offending app] pasted from [other app]. We dont know why some apps collect your clipboard personal and private data, but we can assume that it can be misused for targeted advertising amongst others.
When you open CopyStop, it paste random useless text to your clipboard, so that afterwards you can safely open the app that always tries to "steal" your personal data.
Just starting the app is enough. You can select some default warning texts or funny text to be copied to the offending applications.
Its most useful when it is quickly available, for example placing it in your springboard.