iTunes should not charge your card for anything unless you initiate it.
When downloading Apps its important to understand if they have any recurring subscriptions or in-app purchases. Both of those are detailed in the App's description and details.
You can control free trials and recurring subscriptions by following the steps here: View, change, or cancel your subscriptions - Apple Support
I have been using an iTunes account for many years and have never been charged for anything I did not actually initiate myself.
When I download apps that may have recurring subscriptions, I always check the description, and then go and turn off the auto-renewal as per the link above if I know I won't want it.
As long as you have good management of your account, iTunes should not be applying strange or unwanted charges.