I have a 690 case, so i will try to explain it the best i can from memory...
If the side of the case is off and it is laying down on the ground in front of you, to your right, near the front of the case on the bottom-ish section are small black trays.
To pull the trays out, just sqweez the semi-circular handle and it should slide right out. You should notice on the black tray, around the inside, there are 4 little prongs, those 4 prongs go where the screws would normally go on the HDD. So go ahead and place the HDD in the tray, face up, making sure the prongs line up in the hole.
You should notice the prongs are rubber coated at the base, this is nice because it cuts down on vibration.
Once the drive is in the tray, slide the tray back into position and it should be fine. Connect the SATA or IDE in the back and the power and you're good to go.
If you only have 1 HDD, i would recommend placing it in the center of the rack that way it gets the most air coverage (it doens't ~really~ matter, but it wouldn't hurt) you may also chose to pull out all of the unused HDD trays that you aren't using so they don't block the front intake air flow at all.
Here are some pics to hopefully help, this isn't my CM690, but it's a good clear shot
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