Here’s what consumers have asked with answers from PonyIsland staff and previous consumers.
To both be able to place ponies and items up for Bid/Buy, and to change your account from Trial to Normal, you will need to place a payment to the site. For half a year, it is 14 USD while a Year is 23 USD. After your account is paid for, you can begin placing things for bid/buy, your account will change from Trial to Normal, and you can begin a process called Questing. This will let you sign ponies up for quests, and let you place them in shows to earn levels. Once you have enough levels on your ponies, you'll finish the quest and earn Bonus Points (BP). I hope this helped a little.