what cables do i need im confused

Target display mode does not work on 2019 iMacs.

You have a couple of choices however.

1. Use a regular monitor.
2. Use a 3rd party solution. Such as Luna Display: https://shop.astropad.com/pages/meet-mac-to-mac-mode

For what purpose exactly?

For target disk mode you can use a Thunderbolt 3 (USB-C) cable to connect both computers directly. See here: Use target disk mode to move files to another computer - Apple Support

Thunderbolt 3 (USB-C) Cable (0.8 m) - Apple