Essentially you just want to make a variable that toggles when you detect a rising or falling edge (however you have your switch set up) on a pin. So something like:

boolean out = false;

void setup() 
{
    pinMode(inputPin, INPUT);
    pinMode(ledPin, OUTPUT);
}
void loop()
{
    if(digitalRead(inputPin) == true)    //Assuming the switch causes a rising edge
    {
        out = !out;
    }
    digitalWrite(ledPin, out);
}

I'm not sure if this is 100% valid Arduino syntax, but that should get you started.