Whats The use of function strtok() in PHP, how is better than other string function doing the same thing?

There is no other string function that does the same thing. Functions like explode return the complete split string in an array. strtok on the other hand only returns one piece at a time, with each subsequent call returning the next piece. This is potentially much more economic and memory preserving for large strings.

$addr=strtok($_SERVER['REQUEST_URI'],'?');

but do not call it "better". it's just another way to do it.

strtok is preferred over other function when you have to split a string on more than one delimiter.

The other function that this like preg_split, split are regex based and will have associated overhead with them.