O co chodzi?

This is a bit tricky, because it not only involves type conversion, but some understanding about the way characters are stored and handled in Java. Deep down, a character is always stored as a number representing its position in the unicode table. (You might have a look here, if you hover over one of the symbols with your mouse, you also see the decimal equivalent of the symbol). So every character has a decimal representation (or equivalent) that can be directly stored/converted into an Integer value. If I am not mistaken, the following should roughly be the code of the task before you modified anything:

short liczba = 9; // nothing special so far
char zero = '0';  // this char holds the value '0' also deep down its decimal equivalent, which is 48
// so: println(zero) will give you 0 (as a char), but println( (int) zero) would give you 48 as output
int dziewiec = (zero + liczba);
// Since you store the result of this addition in an Integer, here you add 48 (the int-equivalent of '0') plus 9 which equals 57.
System.out.println(dziewiec); // if you don't change anything, your program will print 57

But have a look at the unicode table again: all we have done is add 9 to the '0'-character, which means: we simply went along 9 places in the unicode table. Luckily, the unicode table has the digits in perfect order and 9 places after the zero, there is number nine again - which has unsurprisingly the decimal value of 57. Now if only there was a way to convert the integer 57 in your print-statement back to its char-representation, which is '9' ... Maybe this helps, feel free to ask questions. Happy Converting!