To get a character, you'll need to answer three questions from any category correctly. At the bottom of the screen, you will find a bar that will fill up as you answer questions correctly. Once the bar is complete (after answering three questions correctly), you will be prompted to choose a category depending on the character you want to win and you will have to answer a question correctly in order to obtain it.
When you spin the wheel, there is also a possibility that you will get a crown. There, you will be prompted to choose the category depending on the character you want to get and you will have to answer a question correctly in order to obtain it.
Once you have obtained the character, the bar will start to fill up again.