Plural and Sentences

I don't know much about grammar rules, and the one problem I have with Is the 's'. Sometimes I get it right but mostly I'm confused. What can I do to better my understanding?

Also, how do I compose sentences? Suppose I have an idea, a theory or something and I want to put it on paper. I have a lot of things on my mind but when I want to write them down it takes me a lot of minutes before I can make it sounds right.

I learn English mainly by observing and remembering the patterns that people use. Since I don't know much about the rules I go by the sound and pause but now would like to really learn the rules.