When I was a kid, the transportation system was very backwarold.

From my hometown to my county city, it's thirty more kilometers awaydistance, but goods were all transported by man powered carts.

For aAlmost all the farmers, they used were using crop straw to make cooking fires, and it seemed like that was the only choice.

My father worked for the local government, so he knew some more thingsbetter than ordinary farmers.

My family were very excited because we knew that coal was more efficient than crop straw used for cooking fires.

In order to get the coal to my home, my brother-in-law decided to go to the county toand get the coal back with a man powered cart.

I asked my brother-in-law if I could go with him and he agreed.

Brother-in-law would be your wife's brother. Is that what you mean?

When we almost arrived inBefore we got to the city, it was already afternoon, and I saw some buildings with two or three floors which I had never seen before.

The tall one that left a deep impression on me was a cylinder that was made of red bricks.

I knew that it was a water tower later.

Later I learned that it was a water tower.

AfterWhen we finished loading coal and returned, it was already late afternoon.

What do you mean by "Returned" here, it is not clear.

My brother-in-law pulled the cart and I walked followinged him.

Around 9 pm, we arrived in athe town.

We ate a few steamed buns and, drank a few bowls of water and fell asleep.

Next morning, we got up early and continustarted to go back home.

In addition, I still can remember how delicious a steamed wheat flour bun was because in my daily life, I was not able to get the chance to eat it, I could only eat steamed sweet potato flour buns.

From mMy hometown toand my county city, it's are more than thirty more kilometers awaypart, but goods were all transported by man powered carts.

My hometown and my county city are more than thirty kilometers apart, but goods were all transported by man powered carts.

For almostNearly all the farmers, they used crop straw to make cooking fires, and it seemed like that was the only choice.

Nearly all the farmers used crop straw to make cooking fires, and it seemed like that was the only choice.

Flows more smoothly this way

My father worked for the local government, so he knew some(a few) more things than ordinary farmers (did).

My father worked for the local government, so he knew (a few) more things than ordinary farmers (did).

My family wereas very excited because we knew that coal was more efficient than the crop straw used for cooking fires.

My family was very excited because we knew that coal was more efficient than the crop straw used for cooking fires.

I added "the" because you're talking about a specific crop straw -- the crop straw used for cooking fires

In order to get the coal to my home, my brother-in-law decided to go to the county to get the coal back with a man powered cart.

In order to get the coal to my home, my brother-in-law decided to go to the county with a man powered cart.
Removed "get the coal back" since we already know he's getting the coal from the first part of the sentence.

Or "In order to get the coal to my home, my brother-in-law decided to go to the county with a man powered cart to get the coal."
When you get something back, that means you already had that thing before and you're getting it again.

My brother-in-law pulled the cart andwhile I sat oin it.

My brother-in-law pulled the cart while I sat in it.

After we finished loading the coal and returned, it was already late afternoon.

Or "It was already late afternoon by the time we finished loading the coal and returned"

I would change it to "It was already late afternoon by the time we finished loading the coal and started returning" because you only actually returned to your home later, based on what I read after.

We ate a few steamed buns and, drank a few bowls of water, and fell asleep.

We ate a few steamed buns, drank a few bowls of water, and fell asleep.

Your sentence is fine if used in a casual setting. I just made it a bit more formal

In addition, I still can remember how delicious a steamed wheat flour bun wais because in my daily life, I wasam not able to get the chance to eat it, I couldan only eat steamed sweet potato flour buns.

In addition, I still can remember how delicious a steamed wheat flour bun is because in my daily life, I am not able to get the chance to eat it, I can only eat steamed sweet potato flour buns.

Changed the tense