An introduction is a beginning section which states the purpose and goals of the following writing. The introduction is usually interesting and it intrigues the reader and causes him or her to want to read on. The sentence

Sentence (linguistics)

In the field of linguistics, a sentence is an expression in natural language, and often defined to indicate a grammatical unit consisting of one or more words that generally bear minimal syntactic relation to the words that precede or follow it...

in which the introduction begins can be a question or just a statement. This is generally followed by the body and thesis statement, or what you're going to talk about.