Do I Have to Purchase the App Multiple Times?

When you purchase an app on the App Store, it’s free to install onto every device that you own.

You can view and re-download all of your purchased apps by doing to the Today tab on the App Store, then tap your profile at the top, then tap Purchased.

You will not be able to install your purchased apps onto devices that are owned by somebody else, your purchases are linked to your Apple ID.