intro
The Linux manual documents intro in 8 places. Pick the section you want.
intro (1)introduction to user commandsintro (2)introduction to system callsintro (3)introduction to library functionsintro (4)introduction to special filesintro (5)introduction to file formats and filesystemsintro (6)introduction to gamesintro (7)introduction to overview and miscellany sectionintro (8)introduction to administration and privileged commands