A program does exactly what the programmer specifies. A sophisticated program written by an experienced programmer can do a lot (correctly), a half-baked program written by a beginner is likely to do simple tasks wrong.
Everything that a computer does is the result of executing one or more
programs. This should give you some idea of what kind of complicated
tasks can be done by a program. In this class, however, we will focus more
on simple programs that are more educational than practical.