The RED LED indicates power is on. If you have connected the battery or attached a Micro USB cable and this LED is not on, you need to press the power button.
The ORANGE LED signals the state of the radio link from a transmitter (TX). When turning on it flashes rapidly in a dimm orange color while waiting for a TX signal (always turn on the TX before turning on the drone and turn the TX off after turning off the drone). When it detects a signal from a TX it becomes solid orange. If it doesn't detect a signal from a TX, it automatically enters Bind mode and flashes rapidly very bright.
The GREEN LED signals the state of the flight controller. Flashing green means disarmed, solid green means armed (ready to fly).
The BLUE LED signals the state of the GNSS. A solid blue means that the GNSS has a satellite fix.