Buy It On Itunes -

Open > Settings > General > Show iTunes Store > Search > Click Price.

Open > Store (sidebar) > Click "Buy" or "Rent". Windows PC buy it on itunes

Depending on what you want to buy, you will use different apps on your device: Open > Settings > General > Show iTunes

Open > Settings > General > Show iTunes Store > Search > Click Price. Open Apple TV app > Search > Select "Buy" or "Rent". Payment & Redemption buy it on itunes

Buy music from the iTunes Store on your iPhone or iPad - Apple Support