Paragraph 1 - introduction
This paragraph has two main purposes: 1) To attract the reader's attention. Have a good, strong opening sentence. 2) To inform the reader what the essay is about. However, do NOT write "This essay is about...," or "I am going to write about..." It is not wrong to start like that, but it's not very good style (ask Paul!). However, you DO need a THESIS STATEMENT which usually comes at the end of the introductory paragraph and explains what the essay is about. For example, if you were writing about the history of Harrods, your thesis statement should NOT be:
"This essay is about the history of Harrods." OR "I am going to write about the history of Harrods."
A much better style of writing would be:
"From its start as a family grocer's shop to its present position as one of London's most prestigious stores, Harrods has undergone many changes." This is a THESIS STATEMENT that informs the reader about the content of the essay.
Middle Paragraphs 2,3,4
Each of the middle paragraphs in the essay should have a TOPIC SENTENCE at its beginning that introduces the contents of that paragraph. Each sentence should then follow logically from the one before. Don't jump around with your ideas.
Again, using the above example of the history of Harrods, the second paragraph might begin:
"Charles Harrod first opened a small grocery store in the East End of London in 1896."
The rest of the paragraph would then be about the early days.
Paragraph 5 - conclusion
This final paragraph should sum up your main points. It's the "And they all lived happily ever after," part of the essay - the end! Sum up what you have said and write a few general statements that draw it all together.
"As can be seen, although Harrods is still a family owned business, it has grown from a small grocery to a huge and internationally famous department store." etc.