First off. Select the SPI interface on the IM# pins.
Connect CS, RS, SDI, SDO pins.
Run the Read_ID_bitbash.ino example to identify the controller.
Then configure your User_Setup correctly. Your link implies ILI9488. So it is unwise to say "ST7796S"
Seriously. It is much safer to buy displays that are already configured and mounted on a pcb. There are less things to go wrong.
When you have developed and tested your project on a prototype (using ready made components) you can design a custom pcb for bare components.
David.