Agent Builder turns a task you keep re-explaining into a named assistant. It creates what Microsoft calls a declarative agent: a custom version of Copilot that follows your instructions and reads only the knowledge sources you picked, such as files, SharePoint sites, Teams chats or public web pages. You describe the job in plain language or fill in the fields yourself, then test it on the Try it tab.
Unlike a Claude skill, which fires quietly when your wording matches, an agent is its own destination that you open on purpose. Every new agent starts private. You can share it with colleagues as Can chat or Can edit, or list it in your organisation's Agent Store. Sharing never overrides anyone's own permissions.