What is the annual tax report?

• What is the annual tax report and what is it for?
• Who is required to file an income tax return?
• Important Dates 
• How is the income tax report calculated?
• When do I have to pay and when not?
• Individual or joint declaration
• How can I purchase the service and what is the price?
• When will my tax report be available?
• My Renta draft says there is a discrepancy between my income and what the Tax Agency (AEAT or Hacienda) has on file. What does this mean?
• Is Renta (annual income tax return) included in my Xolo plan?
• Can I file a joint Renta declaration with my spouse who has no income?
• I registered as autónomo partway through the year. Do I need to file Renta for the full year?
• Does the 'gastos de difícil justificación' deduction apply to me automatically?