Paragraphs are made up of a few sentences. Once you have established your outline with the subheads, it should be easy to write a few sentences about each subheading.
This way you have a few paragraphs under each subhead.
Your words should be original. However you can borrow something and re-write it into your own way of expression. Facts are facts and sometimes you can’t help not saying something someone has already said. However by putting it into your context, adding a few extra words, or changing a couple of words, you can make it your own statement.