The Introduction minimally contains background information and a statement of the purpose; in some fields, the questions to be addressed, as well as the boundaries of the research, are also mentioned.
The most common way to structure an introduction is to start out by setting the topic of the text in the larger context. This background information is then followed by a statement of the purpose of the essay, which is sometimes expressed as a thesis statement. The research questions may be explicitly set out.
After having read the introduction, the reader should understand what the purpose of your study is. That is, what it is that you aim to do in this study.
After having read the introduction, the reader should also understand why your study is worthwhile. Explaining the relevance of your study is sometimes called answering the “so what?” question. That is, you have to explain to the reader why she should care about your study. What is the point of this study? How does this study contribute to our general knowledge and to the research field?
The Introduction as a whole is usually written in the present tense, although a review of background material may be written in past tense.