In Castle Clash, the arena allows your heroes to battle against other player’s heroes. There is 3 lanes(Top, Middle, Bottom) which you can station your heroes. You are allowed to put up to 5 heroes on the starting points, which are those white circles. You can also choose to station them all mid/top/bottom if you would like to.
The objective is to kill the enemy base faster than your opponent. Most of the time your opponent will just stack all the heroes in one lane. It is usually better to just place all your heroes in the middle lane and make a charge at the base.
You can also set up your defensive team and where they will show up in lane. Most of the time, you would just put all your heroes in 1 lane. However, if you have fast heroes like the Assassin or Ninja, you can put them on separate lanes from the other 3 heroes. This way, you can sneak in a win or two if you can get to your opponents base faster.
Winning an arena battle nets you honor badges(40-60) while losing gives you 6 . Either way, you are getting some honor badges. As you win more arena battles, your rank increases and that also increases the amount of honor badges you earn per hour.
I would encourage you to do 10 arena battles a day for 10 gems and at least 60 honor badges. This will help you in the long run as those gems will allow you to hire an extra hero or two.
If I find out that I won’t win that arena battle, I just end the battle so I won’t waste time fighting a losing battle. You will know when you battle players with heroes 20 levels higher than yours.