Step 1: Create a thread in the 'goods' section.
Post all the information that you need.
Take photos of the product with a piece of paper that has your username & the date on it.
Step 2: If someone wants to buy it, both of you must agree on an escrow.
https://bitcointalk.org/index.php?topic=855778.0List of trusted escrow
Step 3: once escrow confirms they are holding the money (make sure you get it verified from the escrow, a lot of people try to scam like this) (oh and escrow means like a middleman) you go out and send the item
Step 4: once buyer confirms they got the item, escrow release money.
You are now a happy seller of your ps4