This is a sample quotation template. You should customize it to fit your own needs from the Sales application, using the menu: Configuration / Quotation Templates.
Great quotation templates will significantly boost your success rate. The first section is usually about your company, your references, your methodology or guarantees, your team, SLA, terms and conditions, etc.
You can set a description per product. Odoo will automatically create a quotation using the descriptions of all products in the proposal. The table of content on the left is generated automatically using the styles you used in your description (heading 1, heading 2, ...)
If you edit a quotation from the 'Preview' of a quotation, you will update that quotation only. If you edit the quotation template (from the Configuration menu), all future quotations will use this modified template.