Knowledge of specific grammatical rules plays a much less significant role than does knowledge of specific vocabulary in knowing a language, as a general rule, but grammar is still a core part of most languages.The structure that grammar lends to the vocabulary can vary dramatically from one language to another. At the core of understanding grammar is the syntax of a given language. Syntax is the way a language orders words in phrases.
Some languages, like English, have a vary complicated word order. These languages require that words in phrases be but in a specific order to communicate an idea effectively.
For example, English requires that an adjective associated with a noun must precede the noun when describing it.
One can say "the tall table" but not "the table tall." Other languages, however, do not emphasize syntax at all.
As long as the words are within a sentence, they can be ordered in any way to retain meaning. Latin, for example, does not require a certain word order to communicate an idea.
Other grammatical considerations, though, must be taken into account in order to understand languages with a simple syntax like Latin. Attaching prefixes or suffixes, as well as adding inflection, can change the meaning of words. Typically, the more advanced suffix or inflection structure that a language has, the fewer syntactic rules there are. The grammatical makeup of any language is a variety of different considerations that may not be an important part of other languages.