First of all, the abstract is an excerpt from the main content of the article, which requires short, accurate and complete. The number of words can be as few as dozens, and it is advisable not to exceed 300 words.

Secondly, preface = introduction = introduction. The introduction should generally write the author's intention, explain the purpose and significance of the topic, and point out the writing scope of the paper. The introduction should be short and concise, and stick to the theme.

Finally, the abstract is before the preface. At the beginning of the whole paper, the preface is located at the beginning of the main body of the paper.

If you don't understand, you can Baidu "paper format".