When you plant your tomato plants, you can remove the lower leaves when planting so you can plant the plant in the dirt.
Suckers are little leaves that reduce sunlight and inhibit the ripening of tomatoes. It is easy to pinch or clip of the small ‘sucker’ leaves like the one you see in this picture to have a healthier plant. They are just a small shoot with leaves out of a stem.
Pluck away but do not get rid of healthy stems that support tomato growth and have tomatoes on them.