Twilio Serverless is used to deploy web apps quickly, and IBM Watson makes it easy to perform various machine learning tasks. The Twilio Serverless Toolkit provides CLI tooling for developing locally and deploying to Twilio Runtime. A Twilio account and phone number with SMS capabilities are required, along with an IBM Cloud account and Node.js installed. To build the app, a new project is created using the Twilio CLI, and the `ibm-watson` library is installed. The Twilio Function is written in JavaScript, authenticating to the Watson API using IBM Cloud IAM, and translating the input message to Gaelic. A public-facing URL can be obtained by deploying the app to the Twilio Runtime.