issue with mp3 code

so i recently discovered arduino and i wanted to make myself an arduino mp3 i searched for tutorial and i found one with component i bought. but i have issues with the code that is given.

#include <SoftwareSerial.h>
#include <DFMiniMp3.h>
void setup () {
Serial.begin (9600);
mp3_set_serial (Serial); //set Serial for DFPlayer-mini mp3 module
mp3_set_volume (10);
}
void loop () {
mp3_play (1); //play 0001.mp3
delay (10000); //10 sec, time delay to allow 0001.mp3 to finish playing
mp3_play (2);
delay (5000);
mp3_play (5);
delay (5000);
mp3_play (20); //play 0020.mp3
delay (9000);
mp3_play (81);
delay (6000);
mp3_play (74); //play 0074 mp3
delay (6000);
}
and here are the error message i have
C:\Users\Titouan\Documents\Arduino\sketch_jan31a\sketch_jan31a.ino: In function ‘void setup()’:
sketch_jan31a:6: error: ‘mp3_set_serial’ was not declared in this scope
mp3_set_serial (Serial); //set Serial for DFPlayer-mini mp3 module
^
sketch_jan31a:7: error: ‘mp3_set_volume’ was not declared in this scope
mp3_set_volume (10);
^
C:\Users\Titouan\Documents\Arduino\sketch_jan31a\sketch_jan31a.ino: In function ‘void loop()’:
sketch_jan31a:12: error: ‘mp3_play’ was not declared in this scope
mp3_play (1); //play 0001.mp3
^
Plusieurs bibliothèque trouvées pour “SoftwareSerial.h”
Utilisé : C:\Program Files (x86)\Arduino\hardware\arduino\avr\libraries\SoftwareSerial
Non utilisé : C:\Users\Titouan\Documents\Arduino\libraries\SoftwareSerial
exit status 1
‘mp3_set_serial’ was not declared in this scope
i relly don’t understand what i did wrong help

I see no declaration of an instance of the DFMiniMp3 class. Have you looked at the examples that come with the library. The examples show how to construct an instance of the class. The API reference also has some information.