How do you unlock all missions in san andreas?

The only information available from the cited source is a general description of Grand Theft Auto: San Andreas as an action-adventure game set in the fictional U.S. state of San Andreas. It mentions that the game is played from a third‑person perspective and that the player can roam freely on foot or by vehicle. There is no detail in the source about the mechanics for unlocking missions, such as story progression steps, side quests, or specific triggers. Therefore, based on the verified evidence, it is not possible to state how to unlock all missions in the game. For information on mission unlocking, one would need to consult additional sources that cover gameplay instructions or the game's user manual.