Yes, you can play as many battles you see on the Map (known as "Training Battles") as you like.

The number of Stars you see in the preview reveals the difficulty of the battle as well as the number of Stars you get upon winning.

            ⭐  1 Star: Easy battles

       ⭐⭐  2 Stars: Intermediate battles

  ⭐⭐⭐ 3 Stars: Difficult battles

Playing Training Battles helps you train your wizarding and battling skills.

However, you will most likely want to complete Quest battles too. Completing Quests embarks you on an amazing adventure where more fun characters and monsters looking forward to making your acquaintance. 

💡Learn more about: How do I start a battle in a Quest?