Your application to the Employment Tribunal, ‘ET1’, is almost always the most important document in your whole case. Most of the form is fairly straight forward. Question 8 can be very difficult to get right. That is where you tell the Tribunal and the other side what your case is about. You need to provide details of everything that you are complaining about without including irrelevant details. I would say most cases that are ultimately unsuccessful would have had a much better chance if question 8 had been answered better. If there is not enough space on the form you can provide your answer in a separate document.
If you fail to include something here at this stage it is very unlikely that you would manage to add it later. Don’t say things like ‘I can provide details later’. This is your chance to tell the whole story.