If you are about to write or extend a Wikipedia article or a Wikibooks chapter as a course requirement, here are the steps you should follow:
Choose a topic. Which article (in Wikipedia) or chapter (in Wikibooks) would you want to write? In case of Wikibooks you should also choose the book in which you would insert your chapter. Let me know about your choice. (Do not forget to tell me whether you'd want to write a Wikibook or Wikipedia material.) We have to be sure that the topic is appropriate for the course, and the same topic was not chosen by others. It is your task to check whether the topic is already available in Wikipedia or Wikibooks.
Write your first draft. If you extend an existing article or chapter it could be useful to copy the original text to a word processor (LibreOffice Writer is preferred) and use change tracking, so it is easy to follow what is the new text you added or modified. In Writer change tracking is available in Edit > Changes > Record. If you have any questions while you write it, contact me. Some advices on writing the text.
When you are ready with the first draft, send it to me. Although we call it first draft, the writing should be its intended final form.
I will suggest modifications in the draft and will send it back. I'll send it in .odt format. You can use LibreOffice to open it safely.
After considering the suggested modifications and possibly rewriting some part of the text you can upload the writing. Send me the link of your work.
Show your work proudly to your friends and family. Also share it on Facebook, etc. ;)
Check the deadlines on the page of the relevant course.
Before starting the work it is useful to read through this tutorial:
http://en.wikipedia.org/wiki/Wikipedia:Tutorial
Introduction
Wikibooks contains textbooks.
You can read about it here:
http://en.wikibooks.org/wiki/Wikibooks:What_is_Wikibooks
and here:
http://en.wikibooks.org/wiki/Using_Wikibooks/What_Is_Wikibooks
Join a book
If you're not planning to start a whole book, you could join others.
Here are some considerations which one to choose:
http://en.wikibooks.org/wiki/Using_Wikibooks/Contributing_To_An_Existing_Wikibook
Plan the parts or chapters:
http://en.wikibooks.org/wiki/Using_Wikibooks/How_To_Structure_A_Wikibook
Create an account
Using an account, your contribution will be more visible.
Find some other reasons why to create an account and how to do it:
http://en.wikibooks.org/wiki/Using_Wikibooks/Setting_Up_A_User_Account
Upload your work
To create a chapter choose a book you want to insert your chapter into. In the titlebar, you'll see something like this: http://en.wikibooks.org/wiki/Title_of_the_book. Extend the address with your chapter name, separating the chapter and the book with the sign "/". Use underscore instead of spaces in the name of your chapter. Now the address should look something like this: http://en.wikibooks.org/wiki/Title_of_the_book/Title_of_the_chapter. Hit enter, and then click on "Start the My chapter page" link.
After creating the page you can edit the text. To format the text you can use the toolbar at the top of the text area.
Some introductory information about editing pages:
http://en.wikibooks.org/wiki/Using_Wikibooks/How_To_Edit_A_Wikibook
You can edit the text more directly with special signs to format it.
Find some formatting methods here:
http://en.wikibooks.org/wiki/Editing_Wikitext
Most of the time a few tools should be enough. Some of the most important methods are:
http://en.wikibooks.org/wiki/Editing_Wikitext/Emphasis_and_Links
http://en.wikibooks.org/wiki/Editing_Wikitext/Indents_and_Lists
http://en.wikibooks.org/wiki/Editing_Wikitext/Headers
http://en.wikibooks.org/wiki/Editing_Wikitext/Pictures/The_Quick_Course
It is easy to look for some examples and previous solutions to see how some problems were solved.
More information
To find a lot of other information about using (reading) and contributing to (writing) Wikibooks you can read
http://en.wikibooks.org/wiki/Wikibooks:Welcome
and
http://en.wikibooks.org/wiki/Using_Wikibooks
Wikibook chapters