Salesforce beginner learning materials

Trailhead main page - https://trailhead.salesforce.com

Apex Basics & Database - https://trailhead.salesforce.com/modules/apex_database

Admin Beginner - https://trailhead.salesforce.com/trails/force_com_admin_beginner

Admin Intermediate - https://trailhead.salesforce.com/trails/force_com_admin_intermediate

Developer Beginner - https://trailhead.salesforce.com/trails/force_com_dev_beginner

Force.com Fundamentals [ HTML | PDF ];

Visualforce Basics - https://trailhead.salesforce.com/modules/visualforce_fundamentals

Visualforce in Practice [ PDF ];

Limits:

• Understanding Execution Governors and Limits;
• Governors in Apex Code;
• Salesforce Limits Quick Reference Guide Overview [ HTML | PDF ];

Useful links:

• Salesforce developer main page;
• Apex Code Best Practices;
• Work with try/catch and assigning errors;
• Triggers and Order of Execution;
• An Introduction to Apex Code Test Methods;
• How to Write Good Unit Tests;
• Testing Best Practices;
• Salesforce.com Certified Force.com Developer.