Your task description will be the organizing principle for the rest of your presentation. Most of what follows will be an account of what you did to complete the task.
One way to come up with a simple, clear task description is to imagine you are writing it for a teenager. How would you describe what you did to someone who knows very little about your work? This can obviously be tweaked depending on the audience, but it is worthwhile remembering that the audience to which you speak will all have their specialties in certain fields. Something that is perfectly evident to you may not be perfectly evident to many in your audience.
This does not mean that a lot of your speech should be taken up by lengthy explanations of what you do. Think of it in a similar way to a film. In most films we have periods of what the directors like to call “exposition”. They lay down the “back story”, telling us why what we are watching had to happen.
Film reviewers are very quick to criticize films which have lengthy spells of exposition, as all we really need are the essential details. We can piece the rest together for ourselves. Take the same approach to explaining the task that you were dealing with. Give the important details, and assume a basic level of understanding.
The result of having these brief explanations is that your wider presentation will then be set in a certain context, and it is in this context where the things you say will make sense. When you have completed the first draft of the presentation or speech it helps to then read over it and see if it would make sense to someone who is coming to the presentation without the information that you have.
Any terms which give space for confusion can then be explained a little bit better so that the audience can follow the presentation. If any remaining confusion persists, then a question-and-answer period can pick that up.