In the world of magic, wizards must learn one important ability – spellcasting. It’s their biggest advantage over other beings. This is why the School of Witchcraft and Wizardry Hogwarts teaches students subjects such as: Defense Against the Dark Arts, History of Magic or Charms.
In the world of Harry Potter GO you learn spells by studying spell tomes scaterred all around the world of magic. Those tomes contain a brief description of the spell itself, proper pronunciation and the wand gesture necessary to cast the spell. Each one of these is a very important factor of casting a spell properly.
Let’s start with the description. For a spell to be effective one must know when to cast it. This is why a knowledge about a spell is so important. When in danger you won’t be able to read all of your books to find out which spell should you use. In stressful situations people tend to forget important facts, this is why you must practice a lot to be prepared for such situations.
Proper pronunciation is more important than it seems to be. Spells to be effective have to be precisely casted. During one of his classes, Ron Weasley tried to cast wingardium leviosa spell and failed horribly. This is where Hermione taught him about the importance of pronunciation. The spell wasn’t succesful because he said lev-ee-oh-SAA instead of lev-ee-OH-sa. This small mistake prevented spell from working.
Next important factor is the wand used to cast a spell. In wizard world you don’t choose your wand, it chooses you instead. This is why connection between the wand and the caster is so powerful and you are unable to use magic wand other than your own. At the beggining of your journey Ollivander will send you few wands for tests. After choosing the proper one for you, you will be able to make use of spell tomes.