What are the differences between strcpy and strcat functions in C programming language?

[SubhanUllah]

#include <stdio.h> 
#include <string.h> 
 
int main(){ 
        char s1[20] = "hello"; 
        char s2[] = " world"; 
        strcat(s1, s2); 
        printf("%s\n", s1); 
        strcpy(s1, s2); 
        printf("%s\n", s1); 
}