To start you need at least the following parts:
Insert the Raspberry Compute Module 3 on its horizontal socket and gently press it until snaps into the final position as shown below:
Insert the bootable microSD on its vertical socket with the label on the on the opposite side on CM3 module:
If you have an USB to serial adapter insert its pins as shown below to have access to the serial console port.
The serial setup is 115200,N,8,1 without software and hardware acknowledge.
Connect the power supply lines in a range of 12 to 24 volt DC using the screw terminals as pictured below. The blue led will turn-on to indicate the power availability:
If you have the serial console wired the boot messages will appear on your serial terminal emulator. If you don't have the console port check the led on the ethernet connector to see if there is any activities and try to reach your board by typing:
Unfortunately the standard Rasbian distribution has the ssh disabled by default so, if you don't have the serial console port you need to enable it placing the microSD on a normal Raspberry Pi and using:
If you have the serial port type this command and follow the info to enable the remote SSH access.
Run you SSH client on your PC and connect to firstname.lastname@example.org using the standard user and password:
Login: pi Password: raspberry
Refer to the official Raspberry Pi doc to know how to use ssh with Raspberry Pi: