I don't see a RX-V733 on Yamaha's site. However, look for a stereo audio input on the receiver. Then use the appropriate audio cable or adapter for the CD player audio out.
Depending on the CD player, you should use either an RCA M/M to RCA M/M (red/white) audio cable or a 3.5 mm headphone to RCA stereo audio cable. (If you don't have a headphone to RCA stereo audio cable, you can use adapters on either side. Examples: 3.5 mm M to RCA F/F adapter to RCA audio cable as above or 3.5 mm M/M cable to 3.5 mm F to RCA M/M audio adapter, depending on which cable you want to use and where you connect the adapter.) After making this connection, turn on the CD player, select the appropriate input.
The connection for an external audio device (like a CD player) is shown on page 31 of the manual for the RX-V773. Even if this is a slightly different model, the image may help. The manual is available from Yamaha on the product page: http://au.yamaha.com/en/products/audio-visual/av-receivers-amps/rx-v773_g/?mode=model
. Click on the Support tab. The direct link to the manual is http://download.yamaha.com/api/asset/file/?language=en&site=au.yamaha.com&asset_id=54075
I hope this helps.