C, 123123 121 bytes
Very naive approach: 3 nested loops.
k,n;main(int c,char**v){char*a,*b;do for(c=n++,a=v[1];*a;a++)for(k=c--,b=v[2];*b;b++)printf(k--?"":||printf("%c%c",*a,*b);while(k);}
Compile, then run the executable with the two strings as parameters.