First, you need to enable referrals in orders. To do so:

Step 1: Visit Setup > Global Settings > Others.
Step 2: Enable Mandatory Referral.

To place an order with Referrals:

Step 1: Go to CRM.
Step 2: Enter the customer's mobile or telephone number in the search field and click Search!.
Step 3: Click the Place New Order button, punch in your customer's order, and click Place Order.
Step 4: Select the referral from the Referral dropdown.
Step 5: Click Confirm. You'll find this order under Delivery Manager > Home Deliveries > Home Delivery Orders.