These terms are commonly used in examination questions. To answer a question properly one must know what they mean!
The dictionary definition of “develop” is “to grow or change into something bigger, stronger, or more advanced”.
In the context of language, it means the way in which an idea or argument can be made stronger or more convincing.
Let's suppose I am giving a speech on the topic “Martians are intelligent”. Initially people probably won’t believe me, they might think there isn't any validity to what I am saying at all. But, if I can refer to scientific data to support my assertion, to first-hand reports by people who have talked to Martians, if I show films of Martians behaving intelligently and if I can show how Martians have built some of the fastest computers the universe has ever seen, then I am developing a powerful argument for my position.
In an exam we may either be asked to develop an idea ourselves or describe how another writer develops an idea.
The dictionary definition of “reinforce” is “to give support to an opinion, idea, or feeling, and make it stronger”.
This is similar to “develop” but the emphasis of the word is on strengthening rather than growth. The argument already exists but needs to be made even more convincing. You can think of "reinforce" in terms of reinforced concrete which is concrete with steel bars in it. This reinforcing makes the concrete much stronger and safer.
If I have already developed an argument that Martians are intelligent I could reinforce my position by quoting another expert, or by bringing along some real Martians to let people see just how smart they could be.
The dictionary definition of “explain” is “to tell someone about something in a way that is clear or easy to understand”.
One can explain what something means, why somebody does something or why something is the way it is. In English we are often asked to explain why or how the writer uses language in a particular way.
So, at the end of my talk on Martians somebody in the audience might ask me to explain why he hadn’t seen any Martians on TV. I would then give my reasons - Martians are camera-shy. Note that I am not developing my argument - I have already done that. Nor am I directly reinforcing my argument. Rather I am helping a person understand something.
The dictionary definition of “analyse” is “to examine or think about something carefully, in order to understand it”.
Analysing is like explaining but at a deeper level. When you explain something you pass on simple knowledge to a person. When you analyse something you come to understand how all the parts of something work together to produce a particular result. Also analysing is something that you do first for yourself, maybe sharing your findings with others later.
I could explain to you how to greet a Martian if I know a few basic words. However before I could speak Martian effectively I would have to analyse the Martian language.
The dictionary definition of “structure” is “the way in which the parts of something are connected with each other and form a whole, or the thing that these parts make up”.
So, when discussing the structure of a piece of writing you will be talking about the parts of it: what parts there are, how they relate to each other and whether there is a pattern in the parts such as repetition. If you identify different parts you may find and discuss whether the different parts have different functions.
Many forms of writing have standard structures. At one extreme Shakespeare's plays are in 5 acts with each act having a special function in the overall development of the play. The essay structure you usually use at school is a 5-part structure where each paragraph has a particular function in the essay. At the other extreme a lot of jokes have 2-line structures:
Q. What do you get when you cross a chicken with a Martian?
A. An eggstraterrestrial!