docs(assistants): add assistants quickstart page

Author: goosewin

fern/assistants/quickstart.mdx

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+---
+title: Assistants quickstart
+subtitle: Build your first assistant and make a phone call in minutes
+slug: assistants/quickstart
+---
+
+## Overview
+
+Create a voice assistant with a simple prompt, attach a phone number, and make your first call. You’ll also learn how to add tools to take real actions.
+
+**In this quickstart, you’ll:**
+- Create an assistant (Dashboard or SDK)
+- Attach a phone number
+- Make inbound and outbound calls
+
+## Prerequisites
+
+- A Vapi account and API key
+
+## 1) Create an assistant
+
+<Tabs>
+  <Tab title="Dashboard">
+    <Steps>
+      <Step title="Open Assistants">
+        Go to the [Vapi Dashboard](https://dashboard.vapi.ai) → Assistants → Create Assistant.
+      </Step>
+      <Step title="Add a system prompt">
+        ```txt title="System Prompt" maxLines=8
+        You are a friendly phone support assistant. Greet the caller and offer help. Keep responses under 30 words. If a transfer is requested, confirm reason first.
+        ```
+      </Step>
+      <Step title="Publish and test">
+        Click Publish and then “Talk to Assistant” to validate behavior.
+      </Step>
+    </Steps>
+  </Tab>
+  <Tab title="TypeScript (Server SDK)">
+    ```typescript
+    import { VapiClient } from "@vapi-ai/server-sdk";
+
+    const vapi = new VapiClient({ token: process.env.VAPI_API_KEY! });
+
+    const assistant = await vapi.assistants.create({
+      name: "Support Assistant",
+      firstMessage: "Hello! How can I help you today?",
+      model: {
+        provider: "openai",
+        model: "gpt-4o",
+        messages: [
+          { role: "system", content: "You are a friendly phone support assistant. Keep responses under 30 words." }
+        ]
+      }
+    });
+    ```
+  </Tab>
+</Tabs>
+
+## 2) Add a phone number
+
+<Tabs>
+  <Tab title="Dashboard">
+    In the Dashboard, go to Phone Numbers → Create Phone Number → assign your assistant.
+  </Tab>
+  <Tab title="TypeScript (Server SDK)">
+    ```typescript
+    const number = await vapi.phoneNumbers.create({
+      name: "Support Line",
+      assistantId: assistant.id
+    });
+    ```
+  </Tab>
+</Tabs>
+
+## 3) Make your first calls
+
+<Steps>
+  <Step title="Inbound call">
+    Call the phone number you created. Your assistant will answer with the first message.
+  </Step>
+  <Step title="Outbound call (SDK)">
+    ```typescript
+    await vapi.calls.create({
+      assistantId: assistant.id,
+      customer: { number: "+1234567890" }
+    });
+    ```
+  </Step>
+</Steps>
+
+## Next steps
+
+- **Add tools**: [Custom tools](/tools/custom-tools)
+- **Tune speech**: [Speech configuration](/customization/speech-configuration)
+- **Structure data**: [Structured outputs](/assistants/structured-outputs)
+- **Move to multi-assistant**: [Squads](/squads)
+