This document provides instructions for installing Oracle Application Express release 4.2 for Oracle Database 12c. Key aspects covered include: - Understanding the multitenant architecture in Oracle Database 12c and how it impacts Application Express installation. - Choosing between installing Application Express from the database and configuring either Oracle REST Data Services, the embedded PL/SQL Gateway, or Oracle HTTP Server. - Required pre-installation tasks like checking database requirements and choosing a web listener. - Post-installation tasks like creating a workspace, adding users, and converting between runtime and development environments.