What is FMLA?

What is the benefit of FMLA to an employee? Must the twelve weeks be taken for only one qualifying reason? When must an employee be placed on FMLA?  Can the employee work while on FMLA? What is an employee's responsibility while on FMLA? What about my medical records?  Is the information kept confidential?
All medical certifications of serious health conditions, whether of the employee or an employee's family member are considered confidential medical records. The Family Medical Leave Act (FMLA) requires that the records be kept separate from personnel files and be maintained in confidence. In addition, the employee's own medical records are subject to American With Disabilities Act (ADA) restrictions. To avoid possible claims, all certifications and other FMLA records should be maintained in confidential medical files. Access should be limited to those with a strict need to know. 
How can I get more information on FMLA?