1. I feel painful in the stomach.

1-1. I feel painful on the stomach.

(Which one is correct?)

2. The first seed was bigger than the second seed at first. However it was afraid of the cold. So it didn't try to go out. It waited for warm weather. However, the second seed wanted to go out. It wanted to see the bright son. So it tried to push its root into the earth. Finally, it could go out of the earth. It didn't afraid of the cold. With courage and curiosity, it tried to open its bud. However, the first seed was eated by a hen. What kinds of lessons can we learn? Though there are difficulties, you should try to get your goal. You have to preapare your bright future studying very hard. If you do not prepare for the future and do not study hard, you can not achieve your goal.

(Would you check the passage and correct errors,please?)

Neither of those sentences are used. My stomach hurts.

I have a pain in my stomach.
I have a stomachache.

Any one of these three would be correct.

At first, the first seed was bigger than the second seed. So it didn't try to go outside; it waited for warm weather. However, the second seed wanted to go out to see the bright sun.
It wasn't afraid of the cold, so it tried to push its root into the earth. With courage and curiosity, it tried to open its bud. Although the first seed was eated by a hen, ( what did the second seed do?)

What kinds of lessons can we learn from these seeds? Though there are difficulties, you should try to get to your goal. You have to prepare your bright future by studying very hard. If you do not prepare for the future and do not study hard, you can not achieve your goal.