Their grammars are not the same. So you must: 1 - Learn phrases (this is most important) 2 - Learn and understand the grammar (join an English class) 3 - Learn the way of speaking everyday (watching movies, news, sports: Disney Channel, Star movies, BBC...) 4 - Talk more (find a partner, a chance of speaking) I'm sure when you will have a "sense", "feeling", you will be surprised when you can say a lot of things (although not always) without thinking much. Don't worry, some native speakers are not good at speaking, they can't even describe their ideas, and a good speaker makes mistakes sometimes :)

You can't!

If you mean culturally rather than grammatically, question is why do you have to?