The TJA1050 CAN Bus Transceiver Module provides the interface between a CAN bus controller and the physical CAN bus differential lines.
KEY FEATURES OF TJA1050 CAN BUS TRANSCEIVER MODULE:
Up to 1Mb/s bus speed
Up to 1000 meter bus length
5V Operation
CAN stands for Controller Area Network and is the standard for use with automobiles to connect all the electronics and sensors together and is brought out to the outside world via the ODB-II interface.
The CAN bus is in fact a good communication bus for many applications that use multiple distributed MCUs which need to interact with each other.
The key features of the CAN bus is that it uses only 2 wires for bus communications and all MCUs connect to these same 2 wires.
This module is mainly handy for providing the interface for connecting a built-in CAN bus controller as found in some of the more advanced MCUs, to the physical differential bus lines that connect the different MCUs on the bus.
The physical bus consists of two end nodes which sit at the two ends of the bus.  A cable of twisted pair wire which is usually shielded connect the two nodes.  For bench-top type use, any 2 wires will work to connect the nodes. 
 As the bus length increases or the environmental electrical noise increases, using twisted pair and adding shielding becomes more important.
The end nodes have a 120 ohm resistor that terminate the two ends of the bus.  Each of these modules have a built-in 120 ohm resistor at location R3.
 
Module Connections
Since this module operates at 5V, if connecting to a 3.3V MCU a logic level translator will need to be used on the RX line going to the MCU.  Using one on the TX line is optional.
The module has the Select pin of the TJA1050 tied to ground which puts the transceiver into the high-speed mode which is the normal mode of operation.
The main MCU CAN controller connection is via a 4-pin male header.  The physical CAN bus is connected via a 2-pin male header.  The headers are shipped separately so these connections can be wired instead of using headers if desired.  The module will also fit the small 2.54mm screw terminals, but the terminal block will hang off the end of the board.
1 x 4 Header
VCC =  5V power
TX=  Transmit data input.  Reads in data from CAN controller and sends to bus lines
RX=  Receive data output.  Reads out data from bus lines to the CAN controller
GND=  Ground, connects to MCU ground.
1 x 2 Header
CANH  =  CAN Bus H connection.  CANH connects to CANH on other modules
CANL  =  CAN Bus L connection.  CANL connects to CANL on other modules