Steam Keys are usually issued immediately (instantly) when payment is complete (also usually instantly), but it may take up to 24 hours.
If your key is part of an order that contains physical items as well, it will be issued when the order ships from our fulfilment centre.
For games on pre-order, the key will be sent on the release day of the game.
You will receive an email with your key.
If you did not receive an email within 24 hours (or on the release day), please check your Spam/Junk box.
Please feel free to raise a support ticket if you have any other issues, or still cannot find your key.