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.
To add page numbering:
On the Pages panel, select a master page from the Master Page window.
Create a text frame to place your page number field and optionally extra header/footer text.
From the Text Menu, select Insert>Fields>Page Number. A hash symbol (#) indicates the page number.
To change page numbering style:
On the Pages panel, select Section Manager.
From the Number style pop-up menu, choose from various standard numbering schemes such as Arabic numerals (1, 2, 3), upper/lowercase Roman (I, II, III, i, ii, iii), alphabetic letters (A, B, C, a, b, c) and more.