Docs: Refresh docs to organize and standardize reference materials. (#18403)

docs/tools/activate-skill.md

@@ -0,0 +1,43 @@
+# Activate skill tool (`activate_skill`)
+
+The `activate_skill` tool lets Gemini CLI load specialized procedural expertise
+and resources when they are relevant to your request.
+
+## Description
+
+Skills are packages of instructions and tools designed for specific engineering
+tasks, such as reviewing code or creating pull requests. Gemini CLI uses this
+tool to "activate" a skill, which provides it with detailed guidelines and
+specialized tools tailored to that task.
+
+### Arguments
+
+`activate_skill` takes one argument:
+
+- `name` (enum, required): The name of the skill to activate (for example,
+  `code-reviewer`, `pr-creator`, or `docs-writer`).
+
+## Usage
+
+The `activate_skill` tool is used exclusively by the Gemini agent. You cannot
+invoke this tool manually.
+
+When the agent identifies that a task matches a discovered skill, it requests to
+activate that skill. Once activated, the agent's behavior is guided by the
+skill's specific instructions until the task is complete.
+
+## Behavior
+
+The agent uses this tool to provide professional-grade assistance:
+
+- **Specialized logic:** Skills contain expert-level procedures for complex
+  workflows.
+- **Dynamic capability:** Activating a skill can grant the agent access to new,
+  task-specific tools.
+- **Contextual awareness:** Skills help the agent focus on the most relevant
+  standards and conventions for a particular task.
+
+## Next steps
+
+- Learn how to [Use Agent Skills](../cli/skills.md).
+- See the [Creating Agent Skills](../cli/creating-skills.md) guide.