This is self-explanatory and is good for new to players to get to grips with game mechanics, during the time you play this mode, get familiar with item effects and your skills.
Be aware that the AI are suicidal and engage you no matter what, DO NOT ever do this in a real match, attacking recklessly is the first step to losing. Also be aware that the AI will heal to full everytime they level up so it can be very hard to take them down at the start when they level up a great deal.
While playing this mode you may want to consider taking a few minutes out and taking a look at what each individual item from the shop does. Remember that you can access the shop from anywhere at all on the map simply by pressing the Y button, but be aware that the farther you are from the shop the more items cost, this is fine on items such as potions, but be wary of the most expensive items such as Bloody Reaper Claws and any of the bottom row items.
Once the round is over you will be taken to the results screen, here you will see that you have gotten a piece of armor and some gold and exp. If you won (you did win right?) then you will see an item come up in the middle of the screen asking you to bid on it. You must type in the amount you wish to bid, which must be more than the show minimum bid, and then hit bid in order to aquire this item. You can also choose to give up and not get the item. At this point you probably can't even afford the item and most of the rewards in newbie mode aren't worth bidding on at your current point so hit give up.
Now try playing the round a few times in order to get a good grip on how the system works and to give yourself a nice little stock pile of gold. You won't be rich yet but you should have a nice little stash for when you start playing for real.