Page numbers are typically added as placeholders to your master pages. For pages adopting that master page, the current page number will be reported automatically.
You can format the page number and set the numbering style using the Section Manager. This manager also lets you create multiple sections (e.g. Preface, Table of contents, Index, etc.) which can be named, have different page number starts and numbering styles.
Page numbers are actually fields as they dynamically update. For more advanced users, page numbers can be incorporated with <Section Name> fields (e.g., 1 Introduction) introduced using the Fields panel.
To suppress page numbering on initial sections (e.g. Contents or Preface) don't assign a master page.