What does that mean, “level”?
https://www.webster-dictionary.org/definition/Level
Define your question. What is the context of it?
In Writer, the concept of “level” is used to define the document structure, its “outline,” through a hierarchy of styles. If you look at Tools → Chapter Numbering you’ll find that levels 1 to 10 are associated to paragraph styles Heading 1 to Heading 10. There is an additional “level” called “text body” used for normal text. You can use, for example, a Level 1 paragraph style to define a chapter heading. Paragraphs with levels 1 to 10 assigned to them will be picked by the table of contents and can be used to create cross-references.
For more specific information, ask more specific questions.
BTW, all this is explained in certain book about LibreOffice Writer …
Similarly, word level is also used for lists to reflect nesting of items. Parameters are controlled in a bullets & numbering dialog equivalent to chapter numbering. But there is a single paragraph style for a list across all levels.
Level is also met in indexes where you can have up to 3 keys levels allowing you to sort your index on primary key and up to 2 sub-keys.
You can also give the word your own interpretation, relevant in your document context, and you mest explain it in order to get useful answer.