/*
Loop
* Lights multiple LEDs in sequence, then in reverse. Demonstrates
the use of a for() loop and arrays.
* http://www.arduino.cc/en/Tutorial/Loop 
*/
int timer = 50; // The higher the number, the slower the timing.
int pins[] = { 2, 3, 4, 5, 6, 7 }; // an array of pin numbers used for LEDs
int num_pins = 6; // the number of pins (i.e. the length of the array)
void setup()
{
int i;
for (i = 0; i < num_pins; i++) // the array elements are numbered from 0 to num_pins - 1
pinMode(pins[i], OUTPUT); // set each pin as an output
}
void loop()
{
int i;
timer=map(analogRead(A0),0,1023,1,50); // The Map function 
for (i = 0; i < num_pins; i++) { // loop through each pin...
digitalWrite(pins[i], HIGH); // turning it on,
delay(timer); // pausing,
digitalWrite(pins[i], LOW); // and turning it off.
}
for (i = num_pins - 1; i >= 0; i--) { 
digitalWrite(pins[i], HIGH);
delay(timer);
digitalWrite(pins[i], LOW);
}
}

What is this part of the code doing? Is there a place I can read more about the fucntions and concepts explored with this line of code?

timer=map(analogRead(A0),0,1023,1,50); // The Map function

int timer = 50; // The higher the number, the slower the timing.

I hope this was helpful.

David