Go to the collection tab at the top of the page and hover your mouse over it. Then go down to the market and hover your mouse there. This will bring up a list of option for you to chose.
1) Buy characters will take you to the market to see everyone’s characters for sale.
2) Private sales waiting will allow you to see the cards which people are selling to you.
3) Current sales will allow you to see the cards that you are selling.
4) The last two show you your sales and purchase history.