语法方面主要没有很大的问题.我觉得还是语气的问题比较多,还有就是很多地方的选词可以选用的更好（这个就不知道是不是因为楼主词汇量不够呢?）
我接下来就按照一句一句的帮你改吧!另外：
(abc) 是不需要的词/句
[abc] 是多加的词/句
adc -> ABC 大写是更改后的词/句
First [of all],social networking (can)* provide[s] the fast and latest information for business expansion.As we know,(business)** people [have] always want(ed) to buy (the) products at a low price and later sell them to a different place AT [a] high[er] price,so they can earn A profit.
想必既然是“First”开头的话,这应该是整篇文章的第2或3段（如果不是就要注意了!除非是回答问题）.
* 这里的can不需要是因为你后面用了“provides THE...”—既然这里用了THE就表示你很确定social network就是最快和最方便的讯息传达工具,所以前面就不需要这个CAN（可以是）了.
** 不需要business的原因是不光光只有做生意的人才会想要低买高卖的啊!另外一点点extra的小贴士就是英语里面的低买高卖的俚语是"buy low sell high",真的有这个说法,并不是中国式英语哦!
For that reason,(some)* MERCHANTS need some information from different places,such as [the] price level of products,to decide what they should invest [in].
* 不是some,而是所有（全部做生意的人应该都需要吧!）
In ancient China,MERCHANTS [have] always WANTED TO BUY (the) goods from a distant place.[However] they want(ed) to know the different price[s] between DIFFERENT market[s] (places).What DID* they do?SOME bind[ed] (some) messages on pigeons' legs,sent the pigeon out TO TRADE FOR THESE INFORMATION**.
* 这里应该是问“那他们做了什么呢?”,因为两者“could”和“would”都是不确定将来应该做什么,所以用did更为合适.后面的一句我也加了some,这个是回答之前的问题,并只是说一部分的人有这么的去做.
** 最后一部分你没有语法错误,可是从写作的角度来看你还是应该在句尾的时候连接到之前你说过的一些.如果像你写的那样结束了话,你并没有写明白你这句话的用意反而加了很多不必要的疑问：把信绑在鸽子的脚上等回复,然后呢?回复是什么呢?等等—这样子.
THIS would TAKE OVER* five days (on pigeon’s flying),and sometimes for PARTICULAR reason[s],such as hunting or weather,THESE information MAY not be received.It WAS** difficult to get the latest information (for business people).
* 会在5天以上
** 注意你还是在说古时候,所以要注意时态
In addition,business would (have) lack THE flexibility to change products they sold when the market price changed.TODAY,because of the development of globalization and social networking,MERCHANTS can [now] collect (the inventory) information FASTER THAN EVER*.
* 比以前更快
PEOPLE can SIMPLY log on Facebook and WRITE ON THE WALL* OF those (people who) providING [the] latest news.With the THESE information,businessES ARE BECOMING FLEXIBLE [and have more opportunity] to expand their business.
* Facebook上面是write on wall,而不是text.Text一般是指手机短信.
Another advantage of social networking is the lower cost of business.Before THE 1990s,social networking was not that advanced and internet WAS PRACTICALLY UNHEARD OF*.
* 意思是“基本上没有听说过的”—当然这是指internet在90年前的情况,因为的确,因特网也是在96,97年才开始普及的.
(Therefore,)* BUSINESSES (still) used (many) [written] pieces of paper to inform worker[s],connect with customers and [to] report business information such as financial INFORMATION to the public.The accumulated cost of the business,such as THE PURCHASE** of printers,ink CARTRIDGES and paper,reduced the profit of business.
* 这里不需要说“所以”（therefore）,觉得之前并不是解释什么原因,而是简略的说明了当时的情况.
** depreciation是降低,下滑的意思,可是用在这里却是感觉你在说“打印机的下滑价值”,和你真正想要说的完全没有关系.所以改过后就是说购买了（purchase）这些东西降低了生意利润.
Now,social networking provides a very convenient platform for businessES.People are working indoors,COMMUNICATING [through the use of e-mails and]* social networkS (software)** such as Facebook to do their jobs.They can ALSO INPUT DATA INTO THE COMPUTER INSTEAD OF PRINTING ON PAPER***.
* email不是一个social network
** facebook不是一个电脑软件
*** 最后一句就有点感觉楼主在草草完事啦!帮你改了一下,input data就是"输入"(input) 内容（data- 包括各种文字,图片,资料等）
这个花了我好久一个字一个字的修改,希望楼主可以采纳! 语法方面主要没有很大的问题.我觉得还是语气的问题比较多,还有就是很多地方的选词可以选用的更好（这个就不知道是不是因为楼主词汇量不够呢?）
我接下来就按照一句一句的帮你改吧!另外：
(abc) 是不需要的词/句
[abc] 是多加的词/句
adc -> ABC 大写是更改后的词/句
First [of all],social networking (can)* provide[s] the fast and latest information for business expansion.As we know,(business)** people [have] always want(ed) to buy (the) products at a low price and later sell them to a different place AT [a] high[er] price,so they can earn A profit.
想必既然是“First”开头的话,这应该是整篇文章的第2或3段（如果不是就要注意了!除非是回答问题）.
* 这里的can不需要是因为你后面用了“provides THE...”—既然这里用了THE就表示你很确定social network就是最快和最方便的讯息传达工具,所以前面就不需要这个CAN（可以是）了.
** 不需要business的原因是不光光只有做生意的人才会想要低买高卖的啊!另外一点点extra的小贴士就是英语里面的低买高卖的俚语是"buy low sell high",真的有这个说法,并不是中国式英语哦!
For that reason,(some)* MERCHANTS need some information from different places,such as [the] price level of products,to decide what they should invest [in].
* 不是some,而是所有（全部做生意的人应该都需要吧!）
In ancient China,MERCHANTS [have] always WANTED TO BUY (the) goods from a distant place.[However] they want(ed) to know the different price[s] between DIFFERENT market[s] (places).What DID* they do?SOME bind[ed] (some) messages on pigeons' legs,sent the pigeon out TO TRADE FOR THESE INFORMATION**.
* 这里应该是问“那他们做了什么呢?”,因为两者“could”和“would”都是不确定将来应该做什么,所以用did更为合适.后面的一句我也加了some,这个是回答之前的问题,并只是说一部分的人有这么的去做.
** 最后一部分你没有语法错误,可是从写作的角度来看你还是应该在句尾的时候连接到之前你说过的一些.如果像你写的那样结束了话,你并没有写明白你这句话的用意反而加了很多不必要的疑问：把信绑在鸽子的脚上等回复,然后呢?回复是什么呢?等等—这样子.
THIS would TAKE OVER* five days (on pigeon’s flying),and sometimes for PARTICULAR reason[s],such as hunting or weather,THESE information MAY not be received.It WAS** difficult to get the latest information (for business people).
* 会在5天以上
** 注意你还是在说古时候,所以要注意时态
In addition,business would (have) lack THE flexibility to change products they sold when the market price changed.TODAY,because of the development of globalization and social networking,MERCHANTS can [now] collect (the inventory) information FASTER THAN EVER*.
* 比以前更快
PEOPLE can SIMPLY log on Facebook and WRITE ON THE WALL* OF those (people who) providING [the] latest news.With the THESE information,businessES ARE BECOMING FLEXIBLE [and have more opportunity] to expand their business.
* Facebook上面是write on wall,而不是text.Text一般是指手机短信.
Another advantage of social networking is the lower cost of business.Before THE 1990s,social networking was not that advanced and internet WAS PRACTICALLY UNHEARD OF*.
* 意思是“基本上没有听说过的”—当然这是指internet在90年前的情况,因为的确,因特网也是在96,97年才开始普及的.
(Therefore,)* BUSINESSES (still) used (many) [written] pieces of paper to inform worker[s],connect with customers and [to] report business information such as financial INFORMATION to the public.The accumulated cost of the business,such as THE PURCHASE** of printers,ink CARTRIDGES and paper,reduced the profit of business.
* 这里不需要说“所以”（therefore）,觉得之前并不是解释什么原因,而是简略的说明了当时的情况.
** depreciation是降低,下滑的意思,可是用在这里却是感觉你在说“打印机的下滑价值”,和你真正想要说的完全没有关系.所以改过后就是说购买了（purchase）这些东西降低了生意利润.
Now,social networking provides a very convenient platform for businessES.People are working indoors,COMMUNICATING [through the use of e-mails and]* social networkS (software)** such as Facebook to do their jobs.They can ALSO INPUT DATA INTO THE COMPUTER INSTEAD OF PRINTING ON PAPER***.
* email不是一个social network
** facebook不是一个电脑软件
*** 最后一句就有点感觉楼主在草草完事啦!帮你改了一下,input data就是"输入"(input) 内容（data- 包括各种文字,图片,资料等）
这个花了我好久一个字一个字的修改,希望楼主可以采纳!