There are 40 pins on Raspberry Pi Model A+/B+/2 B/3 B but only 26 pins on the LCD, so you should pay attention to connecting the pins to your Pi accordingly.
Connect the HDMI Connector to both the HDMI interfaces on the LCD and the Pi.
You should connect the LCD to Raspberry Pi Model B or Raspberry Pi Zero with an HDMI cable rather than an HDMI Connector.
Turn on the “backlight” switch on the back of the LCD.