If your microcontroller has a RGB interface, the DT024CTFT should display an image when IM3 and IM2 are pulled high. The serial interface is only used to change the default display settings if you require something different. Remember that in RGB mode, your microcontroller is supplying the VSYNC, HSYNC, ENABLE and DOTCLK signals as well as 18 bits of RGB data.  Check the ILI9341 datasheet on the website for the detailed timing.

If you want to change any register settings in RGB mode, you can communicate the the ILI9341 display controller through the display serial interface. When IM1 is high and IM0 is low, the serial port will appear similar to a standard 8-bit SPI port using the SDO, SDI, RS/SCL and CS pins. The WR pin will also be needed to serve as a Data/Command (D/CX) pin for the serial port (4-wire serial). You can use a standard GPIO pin to drive the WR pin. If you have a standard 8-bit SPI port, you can use that, or just "bit-bang" the display serial port using any standard GPIO pins. If you don't have a 8-bit SPI port and don't have enough pins to bit-bang 4-wire SPI, you can use 9-bit serial mode and embed the D/CX signal in the 9th bit of the serial stream (3-wire serial). 9-bit serial mode will always need to be bit-banged. Be sure that the #define's in the ILI9341_SPI example code are set to use the same serial port method you are using.

If your microcontroller doesn't have a RGB port, you will need to set the DT024CTFT to MCU mode using the IM pins. You can transfer display data either in parallel or serial MCU mode. Many customers don't have enough pins for parallel mode and get by with just a simple 8-bit SPI port including the D/CX pin. A few customers don't even have enough pins for that and use 9-bit serial MCU mode. Bear in mind that serial MCU mode will be slower and you won't be able to display moving images very well.  However some customers are okay with this.  You just have to try not to do full screen redraws.