Hi there!
I'm not sure if you already have this but there is a library with pre-loaded sketch examples which show you the different functions of the device being used, in this case your LCD screen. Below is a link to the library. Once on the page, click on the green button that says "Clone or Download" and click "Download Zip".
You can then add the library to the Arduino IDE by going to Sketch->Include Library->Add .zip Library and browse to wherever the library zip was downloaded to.
After this, you can go to File->Examples and look for the library you downloaded and added. There will be the example sketches I mentioned earlier.
Link: GitHub - adafruit/Adafruit_ILI9341: Library for Adafruit ILI9341 displays