It depends on the app, really. If the app verifies the purchase server side, there’s nothing you can do to bypass that. But if the app you wanna crack is just a game that doesn’t need internet, it works 9/10 times. With root, it works pretty much 10/10.
Honestly the best guide is within lucky patcher itself. Open luckypatcher and then tap on the question mark icon in the top-right corner. There you’ll see an explanation of all of the features within luckypatcher. There’s also a guide for creating your own custom patches.