Hi Chief,
If you want to disable in-app purchases on your device, you can click on the "Settings" button, then press "General" and in the "Restrictions" tab make sure that restrictions are enabled. You can then disable in-app purchases by clicking on the relevant line.
If you want a password to be requested every time you make an in-app purchase, please make sure that the "Request Password" setting, just below "In-App Purchases", is set to "Immediately”.
I hope this helps.
Clash on!