Could you please advice how to use the decode().
Just like this:
while(gpsSerial.available()) { // check for gps data
if(gps.encode(gpsSerial.read())) { // encode gps data
gps.get_position(&lat,&lon,null); // get latitude and longitude
Except that I'd store the character and print it, too. And, I'd position the curly braces better. And, I'd ditch the comments that add no value.
while(gpsSerial.available())
{
char c = gpsSerial.read();
Serial.print(c);
if(gps.encode(c))
{
gps.get_position(&lat,&lon,null);