Imagine that it's spring. The birds are chirping, the flies are getting in through the window, the plants are budding their newborn leaves. Now, imagine that you want to tell someone about it all. First, you need a topic sentence to begin the conversation; maybe something like: 'You wouldn't believe how beautiful the birdsongs are this year,' or 'My Gosh, there must be at least a million flies coming in through the kitchen window' or 'The trees and the bushes are bursting with green.'
Now, in order to continue the conversation, you will need to have supporting details that include examples of what you are talking about. You might describe the birdsongs, using examples of the most beautiful songs. You might describe the flies, using examples of where the majority of the flies have landed, or describe the trees and bushes using examples of particular trees or bushes that are most lush and green. These are your supporting sentences. Then, you need a statement that emphasizes the importance of birds chirping, flies getting in and the new green leaves. It might be something as simple as 'I could listen to birds singing forever,' or 'I have got to get some fly strips' or 'Man, am I glad spring is finally here!' These are your concluding sentences, and they emphasize the importance of the birdsongs, flies and new green leaves.
In writing, the body paragraph is the main part of your essay or paper. Each body paragraph contains a topic sentence that tells readers what the paragraph is going to be about, supporting sentences that discuss the idea or ideas in the topic sentence using examples and/or evidence to support that discussion and a concluding sentence that emphasizes the importance of the supporting examples or evaluates the connections between them.