You've come to the right place for everything related to designing and building CommCare applications!
Start with the Application Building Tutorial Series to get a feeling for the app building process. Then check out applications designed by other organizations and review best practices for designing effective and useful apps. Finally, get a list of key references and tools to keep on hand as you build out your CommCare application.
Introduction
Terms and Concepts - the CommCare glossary
App Building Tutorials
Core Information
Form Builder - overview of the form designer, a tool you can use to create forms for CommCare
Errors building an application - help in interpreting error messages while building applications
Manage Applications
Design
CommCare Exchange - Starter Apps - a set of example applications, curated by Dimagi
Application Review - a checklist of design and quality issues to make sure you've considered
Language Support - how to manage multiple languages in your application
Language configuration (for Applications)
Form Bulk Translation (for forms)
Advanced Resources
Case Management
Workflow Support - best practices for common workflows
Referrals in CommCare
Advanced Tools
CommCare Localization Tools (Ethiopian Calendar for CommCareODK)