That is an often asked question on this forum and it is always answered the same:
You have to use Serial.begin(115200); (or any other baud rate) in your setup().
Please use the search function - it does work 
e.g.
That is an often asked question on this forum and it is always answered the same:
You have to use Serial.begin(115200); (or any other baud rate) in your setup().
Please use the search function - it does work
e.g.