Many people say that don't trust the Internet, there are many cheaters (what do you mean by cheaters).

But here, I find many people are friendly to me, they've corrected my writings, and given me some (good/great) advices.

It's hard to find this in real life, I haven't met many helpful people as they tend to be more vigilent (not the right word, maybe "cynical" or "suspicious"is what you mean). They tend to think that helping others will somehow hurt themselves.

Just like the News, an old woman was fall fell down, and a kindhearted person come came to help, the old woman said it was the woman that bumped into her.

Since that,people are afraind of helping. (This isn't a reason, but an example.)It's things like this that show people are afraid of helping others.

I'm so glad to know this site and the people here, I feel as if it's a big family, we help each other and don't expect returns, it's really great!

When I am here, I am happy. Or "When I'm here, I'm happy."

Many people say that they don't trust the Internet, because there are many cheaters online. (You need the pronoun here because you have two verbs, so need two actors, even if same person. Also need the, because the internet is a singular thing.)

However I have found that many people on here are friendly when they correct my writing and they sometimes even give me advice. (You do not need plural for writing and advice. As this site's users are the main object of conversation, you want them at the end with here included there. :)

It's hard to find this kind of helpfulness in real life, because people are more guarded in the real world and they believe helping others will only hurt themselves. (I have put helpful in place of feelings because feelings did not really fit and was only doing job of helpful anyway, plus this makes the writing more concise. Guarded is more appropriate than vigilant in my opinion, because can mean defensive and acting for self-preservation over others. Finally, this is a belief, not thinking. Thinking is the process of thought, while belief is a kind of thought you have without proof. Understand? ;))

On the News there was a story about an old woman who had fallen down and when a kind person helped her up, the old lady said it was the woman who knocked her over in the first place. (The news has news stories. I made this pp because about past act which is import now. Remember your pronouns. Finally the bolded part is a common British English phase for this position, I will explain the meaning in my next PM. :)

It is due to acts such as these, that people are afraid of helping others. (That one event would not make everyone in the world afraid of helping others, so it is not the 'sole reason' (or single that act caused the problem) but is an example (event which shows the problem.) Does that make sense?) :)

I am so glad that I have found this site and met many wonderful people here, because it feels like a big happy family, where we help one another. (Though you know 'of' the site, you would not say in Chinese I know the site, as that implies you know the site personally, which is impossible, because it is an object. :) I also again made it PP and added in wonderful because shows you believe the people are good. :)

When I am here,I am happy. (Remember in English, there are no gaps between the last word and the punctuation marker.) Otherwise, yay to none abbreviated form. :)