Original

A story about a poor man

One day, I walked through the metrol station, I saw a poor man who wore dirty clothings, seemed that he had a mental problem, was seating nearby the metrol station. He picked lots of cigarette bottom and played it. Furthermore, a man passed by who was from Africa i guess bought some food from Mcdonald and gave him, put that on the ground, it seemed that he had no reaction when the African did, it's though-provoking, I tried to walk slowly and noticed what's going on, at the end, he was still playing the cigarette and didn't eat the food.

Correction

A story about a poor man

One day as I walked through the metrol station, I saw a poor man sitting nearby who was wearing dirty clothing and seemed that he had  to have a mental problem, was seating nearby the metrol station.

He picked up lots of cigarette bottom butts and played with them it.Furthermore, there was a passing  African  man passed by who was from Africa  who I guess had bought some food from Mcdonald's and gave it to him, put that by putting it on the ground. But  it seemed that he had no reaction when the African did that. It was though-provoking. I tried to walk slowly and noticed take note of what's what was going on, but at the end, he was still playing with the cigarette butts and didn't eat the food.

Note: I have rearranged the structure of some of your sentences to make them briefer. As a guideline, an English sentence is about 20 words, much longer than that and most readers tend to glaze over.

But it is only a guideline and can be broken with experience.

Try to use adjectives rather than phrases in descriptions.

For example - a man passed by who was from Africa  becomes  a passing African man

the bottoms of cigarettes are butts.

Some word choices are close but not correct - seating -> sitting

However please note that spoken English and written English are different beasts.

Spoken English is very flexible and speakers basically  throw away rules, writers are more rule bound.

You wrote an enjoyable essay, good luck with your studies.