The Introduction is a 20-minute long machinima that tells the GTA: San Andreas' characters' story before CJ's mother's, Beverly Johnson, death. We can tie loose ends there, like Pendlebury's death, why Big Smoke and Ryder betrayed the Families, what CJ was doing before getting back to Los Santos, and why he knew about Salvatore Leone before meeting him, etc. I strongly recommend seeing this machinima as it is well-produced, and it will help you easily understand the GTA: San Andreas story.