A technical document is a written material on any technical topic. The manner of writing differs so much from the usual literary writing. Its primary aim is to help readers, understand what they do not know yet, help them solve a problem, and or persuade them to do an action. What is distinct in a technical document aside from its format, style, and organization is that its content is about technical subject. Remember, technical knowledge is information common to experts and specialist, but not to the general reader. Writing a technical document yourself, would mean you need to learn and think like what experts know about thier fields.

I hope this helps you. Try writing something about science and technology to get you started.