stop();

var nInterval = setInterval(Play, 5000);

function Play() {
clearInterval(nInterval);
gotoAndPlay(_currentframe+1);
}

so what does Every line mean …

stop();
//stop at your desired frame .

//Build the interval
// 1 second = 1000 milliseconds 1 x 1000
// setinterval(the-function , time[in milliseconds])

var nInterval = setInterval(Play, 5000);

/*function which will excute and clear the interval & Will play the next
Frame after 5 sec.*/

function Play() {
clearInterval(nInterval);
gotoAndPlay(_currentframe+1);