i have a hard time understanding to write essay and start paragraph
DO NOT start any paper's first draft by writing the introduction! How can you introduce a paper that you haven't written yet?
Follow the writing process, whether you're writing for science, history, English, or whatever:
Prewriting: brainstorm, research, plan, outline, thesis statement
Writing: write first draft by starting with section II of your outline; write introduction after the body of the paper is written; write the conclusion last.
Polishing: revise, concentrating first on the body of the paper, then the intro, then the concl (revision = making sure ideas are logical and sequential and support your thesis); proofread (spelling, grammar, usage, etc.)
Do you have a thesis yet? Have you done your brainstorming (and maybe research) yet? Have you written an outline?
http://leo.stcloudstate.edu/catalogue.html#org
from http://leo.stcloudstate.edu/catalogue.html
http://www.angelfire.com/wi/writingprocess/