AppScript Problem using GmailApp.SendEmail function

Background:
I’m currently taking a Visual Programming class where we use Google Sheet/ AppScript to create a simple system using triggers and function.

Problem: I’m trying to mimic and create a simple online ordering system where it will send emails to customers once our “restaurant” receives, preparing and delivering their order using GmailApp.SendEmail function. I put some functions on the AppScript but I just cant get what I want to do in code. Here is what I have so far: ( I created a custom menu for each function. For example, once “Preparing Order” button is clicked, the customer will receive an email stating that their order is being prepared”

function prepareOrder(){

// send msge to customer that a Kitchen is preparing the order
// 


}

function completedOrder() {
// send msge to customer that the Kitchen has completed the order 
// 
}

function readyForDelivery()
{
// send msge to customer that the delivery person is preparing the order for delivery 
// 
// 
}

function deliveredOrder() {
// send msge to customer that the order has been delivered and completed with a receipt
//
//  
} 

Goal: As mentioned before, Im a beginner at this and my path is probably silly but my goal is to somehow automate and grab customer info (email) from the spreadsheet to then use that information to send an email and create a receipt/invoice of their order.

AppScipt_SS

Spreadsheet_SS