The HM-10 is a readily available Bluetooth 4.0 module based on the Texas Instruments CC2540 or CC2541 Bluetooth low energy (BLE) System on Chip (SoC).
This specific unit is for sending and receiving data from a Bluetooth Low Energy device to the Rx/Tx lines as a transparent connection. It can be used to send commands from your smart phone to an Arduino for example with the Arduino Rx and Tx connected to the Tx and Rx lines on the Bluetooth module.
Default pin is 123456 device appears as MLT-BT05 - make sure your smart phone or other device supports BLE. Default Rx and Tx settings are 9600-8-N-1.
The I/O lines are 3.3V - use a resistor divider or level converter to communicate with 5V I/O lines. The module has a 3.3V regulator so it can be powered by 5V.