How to write a decent report introduction on work you have created?
First and foremost, despite the conventional wisdom to the contrary, it's actually often entirely acceptable to write technical documents in the first person.  Unless you are specifically required to avoid it, it's OK.  Furthermore, even if you can't keep it, you can always start by writing in first person, and then transform to passive voice later.

From there, a good general skeleton of an introduction is sort of a "cone" funneling a reader towards more specific information:


What is the context for the work that you have done?
What was the goal for the work?
What exactly did you accomplish, and how can it be quantified and verified?
What are the implications of this work?


Finally, if a piece of work is genuinely simple, it's OK if the introduction is quite short.  I have written some reports whose introduction went on for many pages, and others that were a single paragraph, depending on what needed to be explained and in what detail.