Syntax refers to the rules that govern word order. In English, word order affects meaning. In the example:

John kicked Bryan.

John is the subject (or agent)  is performing the action. Bryan in the example is the object. placement of "Bryan" after the verb indicated that he is the one being kicked. By changing the word order,  the meaning changes:

Bryan kicked John.

Not all spoken languages use word order in this way. Some (e.g., Latin) use affixes to indicate the function of the words. Likewise, the nature of signed languages allows some verbs to be directional. That is, the orientation of the hand and movement can be used to show the relationship between agents and objects.