The Arduino Leonardo is a microcontroller board based on the ATmega32u4. It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.
The RC522 is a 13.56MHz RFID module that is based on the MFRC522 controller from NXP semiconductors. The module can supports I2C, SPI and UART and normally is shipped with a RFID card and key fob. It is commonly used in attendance systems and other person/object identification applications.
The DRV8825 is a Motor Driver with two H-bridge drivers and a microstepping indexer. The driver has a maximum output capacity of 45 V and ± 2.5 A. It can operate bipolar stepper motors in full, 1/2, 1/4, 1/8, 1/16 and 1/32-step modes. This driver module is generally used in Robotics, ATMs and Gaming Machines.