Start from left to right. But, do not worry. You will get a sense while moving from one balloon to another.
In this graphic novel, I have used mainly three balloons and only once a fourth type.
The caption balloon brings the voice and narration of the author. It is usually a rectangle-shaped figure.
The speech or dialogue balloon is the voice of the characters in the graphic novel.
The exclamation balloon, a spike-shaped figure, is usually used to describe strong emotions, tense conversations, or sound effects.
Lastly, the fourth balloon, I used only once, at the beginning of the grandpa's memories, to set the idea of recounting memories from the past. As you will notice, during grandpa's past memories, I have used the speech balloon to feel the story as it is occurring in the present.