In conversation, people don't pay close attention to grammar, but writing is VERY different. Grammar is very important for writing, so writers need to learn a little about grammar.
Four important points:
1) Many English speakers (people in the US, Canada, the UK, Australia and New Zealand) don't like grammar and don't understand it. That is because many of their teachers didn't teach REAL English grammar. Grammar makes some people feel stupid ("I only speak English, but my teacher says my grammar is wrong. I must be stupid!")
2) Real English grammar (based on Modern English) is different from old-style school grammar (based on Ancient Latin). Latin grammar is difficult and it makes many people feel stupid. Real grammar DOESN'T make you feel stupid. A very good place to learn Modern English grammar is the free Internet Grammar of English, prepared by University College, London. This was published about 15 years ago.
You can also find the Internet Grammar of English in a Chinese version:
