Arduino UNO uses ATMEGA328P-PU microcontroller and this controller comes pre-loaded with a Arduino UNO bootloader. Basically bootloader is a little piece of code that allows you to program the flash memory of the Arduino’s atmega328p via serial or USB instead of using an ICSP programmer.
HT12D is a decoder integrated circuit that belongs to 212 series of decoders. This series of decoders are mainly used for remote control system applications, like burglar alarm, car door controller, security system etc. It is mainly provided to interface RF and infrared circuits. They are paired with 212 series of encoders.
This is Speed Measuring Sensor Groove Coupler Module For Arduino. The DO output interface can be directly connected to a micro-controller IO port if there is a block detection sensor, such as the speed of the motor encoder can detect.