The same as people have a dominant hand or foot (they are left handed, or right handed) people normally have a dominant eye. Most people have a dominant right eye.
To check which aye is your dominant eye, you must make a simple experiment:
Look at something at a distance with both eyes open, and then enclose the thing you’re looking at in a circle (made with your fingers) placed in front of your eyes.
When you have it done, first close one eye, and see what happens. Then close the other.
When you close one eye, the thing stays inside the circle. With another eye, however, it gets out of the circle.
The eye that you have closed when the object moves out of the circle is your dominant eye.