Ipad as a second monitor

danellys wrote:

How do I turn an ipad into a second monitor to a MacBook Pro? Is it free? Do I have to download additional apps to complete this task? Which wires will I have to buy?

Here is how to: Use an iPad as a second display for a Mac - Apple Support — what Apple calls Sidecar is free, built in, and can be wireless.

As a potential (and also free) alternative to Sidecar, see: Universal Control: Use a single keyboard and mouse between Mac and iPad - Apple Support