Every language has its set of rules determining the manner in which the words constituting a given language's lexicon are put together to form meaningful sentences. That's known as 'grammar', being actually a broader term covering areas such as syntax, punctuation, inflection etc.
Learning the grammar is as important as learning any other aspect of the language, if it's the learner's intention to use the language correctly.
You can, of course, try to neglect the grammar and concentrate on communication instead. You may even succeed at times, since English belongs to the group of languages that tend to be forgiving as regards grammatical incorrectness and its influence on the process of conveying the meaning between interlocutors.
Be careful, though. The assumption that it is possible to speak English incorrectly and still be understood is a false one. Surely, the sentence 'He often come late' is gramatically incorrect, with the third person singular 's' missing, but its meaning is clear to any native speaker.
However, if you say 'I'm here for two weeks', the lack of a proper grammatical structure makes your statement ambiguous, to say the least. The person you are talking to will wonder whether
- You've been here for two weeks,
- You are going to stay for two weeks,
- You are in the middle of a two-week stay.
Additionally, by speaking and/or writing in English correctly, you show respect to the people whose mother tongue is English (the same applies to learning and using any other language, of course).
There are situations when the ability to communicate in a foreign language is of paramount importance and comes before correctness (e.g. at an early stage of a language study), but that should be treated as a temporary solution only and should by no means prevent such an individual from improving their command of the language.
Just my two cents.
- For Teachers