The Auction House can be accessed by talking to Auction Manager Kim who is found on your school grounds. Ask her to see the auctions and she'll open the Auction Window shown below.
To put an item up for bidding, click the "Register" button at the bottom of the Auction window. It will open up your Inventory and the item registration window.
Left-click the item in your Inventory that you want to put up for auction. Only tradeable items can be auctioned.
Enter a Starting Price (minimal bid) and Buy Now price (instant buy out), both have to be over 100 Mar. Then choose how long you want your item to stay listed in the auction house. The fee will change depending on the Auction Period you selected.
After clicking "OK" your item is now listed on the Auction house. You can check on your items by checking the "My Registered Items" box on the lower left of the Auction Window.
If the item is sold, or the auction ends without it being sold, you will receive a mail with the item(s) and/or money.
To bid or buy an item, first find the item you want. You can filter the auction list by using the "Search Condition" section on the left of the Auction Window. Hover your cursor over the icons of the items to see their description and stats.
Click the item you wish to own. Then click "Buy Now" to purchase immediately with the price listed in the Buy Now column, or "Bid" to join the bidding.
Current Price: the current highest bid.
Buy Now: buy out price.
Valid Amount: minimal bid you need to make.
Fee: fees taken by the Auction House.
Amount: the amount of Mar you have.
Expense: final amount that will be taken from your character when the bid is placed.
Bidding Price: enter the max. amount you're willing to bid for the item.
Note that after placing a bid on an item, you can no longer bid again or use the Buy Now option on that item until the auction is over.
If you win the bid, the item will be sent to you by mail. If you lost the bid, your money will be refunded by mail minus the fee.