First things first, let's get a new Firebase project up and running. Head over to the Firebase website and sign up if you haven't already. Once you're in, hit the 'Go to console' button. From there, click 'Add project', give your project a name, and agree to the terms and conditions. Easy peasy!

Next up, we need the Firebase CLI to deploy our Cloud Functions. Make sure you have Node.js and npm (Node Package Manager) installed on your system. Open your command prompt or terminal and type in:

npm install -g firebase-tools

This will install the Firebase CLI globally on your system.

Now that the CLI is installed, let's log into Firebase. In your command prompt or terminal, type:

firebase login

You'll be prompted to log in with your Firebase account. Just follow the instructions on the screen.

Navigate to your project's directory and initialize Firebase with:

firebase init functions

During this step, you'll be asked to select the Firebase project you created earlier. Just pick the right one from the list.

After initialization, you'll see a 'functions' directory. Open 'functions/index.js' and start writing your Cloud Function. For example, to handle user onboarding, you might want a function that triggers when a new user signs up.

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.newUserSignUp = functions.auth.user().onCreate(user => {
  // for background triggers you must return a value/promise
  return admin.firestore().collection('users').doc(user.uid).set({
    email: user.email,
    //...
  });
});

In this snippet, when a new user signs up, their data (like email, uid, etc.) is saved in Firestore. Pretty neat, right?

Finally, let's deploy your Cloud Function. Use the following command:

firebase deploy --only functions

Once deployed, the function will run whenever a new user is created, automating the user onboarding process.

Remember, Firebase Cloud Functions can do a lot more than just handle user creation. You can set up various triggers to enhance and automate your app as needed.