Wiki pages help team members to work together. These pages can consist of project documentation or instructions to work on a project such as coding guidelines, and so on. Initially, you will get a blank template by clicking the Create Wiki button, as shown in the following screenshot:
Creating Wiki
From the Create Wiki page template you can add as many pages as you want. Wiki pages support for markdown: https://docs.microsoft.com/en-us/vsts/collaborate/markdown-guidance?view=vsts.