You mean a transition. Well it depends on what you're writing about... It is basically anything that connects the two paragraphs so it flows. Basically your essay shouldnt be comprised of paragraphs that can just be removed and shifted. There should be a flow.
Read more and then write. It really helps. You accumulate your word stock, learn how you use different phrases, idioms, and so on. Also look through good writing examples or order them here . It's quite easy to learn writing but time-consuming.
You don't put a link in an essay? Why would you? You can reference the link (the person who wrote whatever it is) and then make a reference page.
no, linking one paragraph to another? using a teel structure? T-opic sentence E-xplanation E-vidence L-ink