Wonderful in-depth setup by step instruction to configure ADFS Claim based authentication for SharePoint with cross forest authentication by Jay Simcox from summit7systems.com

Part 1: The Beginning

Part 2: Installing and Configuring AD FS 3.0

Part 3: Configuring SharePoint 2013 for ADFS

Part 4: Troubleshooting

Part 5:Authentication Across Multiple Forest