Having completed your new PC, take some time to go back over your work in the previous steps, and check that all your connections are correctly aligned and secure, and that your CPU, RAM and cards are all secure in their fixings. A thorough check here can save a lot of frustration later on.
Proceed now by connecting the remaining devices, such that you can power up and test the new machine. Position the PC case such that you have clear access the sockets/connectors at the back.
Take the Monitor display cable, and connect it to the suitable connector on the Video Card backplate. Use the cable screws if necessary to fully secure the cable. Don't worry about any other connectors on the Video card at this stage.
Connect this to the 'SPK' socket. It can be found either on your sound card, or if your Motherboard has a sound card built-in, refer to its manual for the correct method of connection.