How can I make list that begins from 2.1?
… and there is not 1.1, 1.x anywhere in the document?
Do you want a pure Numbered List, or do you want use the Chapter Numbering feature?
Please be more descriptive. Start by mentioning OS name, LO version and save format. When it comes to list numbering, you bump into the least compatible feature between .doc(x) and .odt (native format).
Update your question (this is not a forum, it is a Questin & Answer(s) site: a question is editable), don’t use a comment. It is more contributor-friendly to group all needed information at a single location.
Tell us your familiarity with styles. If you don’t know what this is, I recommend you read the Writer Guide for an introduction to this founding principle of Writer.
How do you create your list? If you do this with a toolbar button, you’ll need two mandatory extra steps (configure starting number and restating numbering).