The grammar of Chinese is simpler than that of English.In Chinese the smallest unit which has meaning is character. And in English is word. Some characters can be used independently others can be used only when combined with other characters. We call them words when the units having meanings composed by more than two characters(but for some funtional characters we also call them words, for example 的，了， 地etc are auxiliary words). There are no articles, no plural forms of nouns, no comparative and superlative forms of adjectives,no paticular tenses,etc in Chinese. All those can be indicated by different combination of Chinese words. The important principle in Chinese is that the form of characters cannot be changed in any situation at any time, not like in English the form of words should be changed under different situation. For examples:

I talked to Tom. 我和Tom 谈了。

I will talk to Tom. 我将和Tom 谈一下。

I have talked to Tom. 我已经和Tom谈了。

"谈“means "talk". The form of "谈“ didn't changed into other forms but "talk" did in above examples. "了“ is an auxiliary word. “将“and "已经“ are adverbs. In Chinese those auxilliary words and adverbs can be used to indicate the "tense" which is a little different with that in English. More information on those words will be talked later.

Generally the logic sequence of different parts in a sentence can be expressed in this way:

(When)(where)subject +predicate+object 　or 　(when) subject (where) +predicate+object 　or 　subject (when)(where) +predicate+object

For examples:

上星期天在地铁站我看到了Tom.

上星期天我在地铁站看到了Tom.

我上星期天在地铁站看到了Tom.

Above three sentences all mean : I saw Tom at Metro station last Sunday.

Important notice: 1. In Chinese the position of "when"or "where" , either of them, is before that of predicate.

　　　　　　　　2. When there are"when" and "where" , "when "should be put before "where" .

Anyway, variation in Chinese is little but combination is abundant. Building large enough Chinese vocabulary is very important in learning Chinese.