Second-level title: the title serial number is "(1)", which is the same as the font size of the text, and it is a special line with no punctuation at the end.
As for the first-level title, as the name implies, it is the chapter name of this chapter. The second-level title, equivalent to the numbers in the paper: 1, 2, 3, is the name of the section in this chapter. Similar to the numbers in the paper: 1. 1,1.2,2.3.
A paper generally consists of title, author, table of contents, abstract, key words, text, references and appendices, some of which (such as appendices) are dispensable.
The composition order of the paper is: title, author, abstract, keywords, English title, English abstract, English keywords, text, references, appendix and thanks.