Appwrite and SendGrid are used together to send welcome emails using Appwrite's Cloud Functions. To start, create an Appwrite instance by installing it from Docker or through a digital platform like DigitalOcean or GitPod. Set up a verified sender and API key for sending emails. Write a cloud function using the Appwrite CLI and Java runtime. Use SendGrid's Java SDK to draft and send an email with custom content based on event data, such as user creation. Deploy the function and configure environment variables and triggers before testing it by creating a new user and checking their email inbox. With this integration, developers can use SendGrid's Java SDK to automate welcome emails for users in Appwrite applications.