If you're unsure how to structure your essays, the most important thing to do first of all is to think about what the question is asking you. In A Level History, most questions will ask you to analyse the importance of a factor or turning point - so identifying this should be the first thing you do. Once you've decided on it's importance, try to break up your essay into three sections. Are there other factors you can compare it to? Can you answer the question in terms of themes (such as social/economic/political)? Or is the question asking you to compare two time periods or 'turning points'? Once you've identified your three sections, write a sentence under each heading summarizing it's importance, relating the factor/theme to the question. Then try and think of some evidence from your revision or notes that backs up your opinion. Once you've done this for all three, take a step back and have a look at what you've got so far. You should have the beginnings of an argument forming - write down the key points of your argument, and this should form the basis of your introduction. Of course, this is a very specific way of tackling and structuring your answer - and there are many correct ways of going about answering history essays. But if you're stuck with structure, this is a good way to start - by ensuring you're thinking logically about the question and what it's asking of you, you should be able to write a neatly structured and solid essay.