The symbols that are present in numerical expressions are ( ), [ ], y6, x, -:-, -, and +. 

What do they mean? 
The symbols in a numerical expression’s definitions are ( and ) are parentheses which you use to group a problem or number to make a problem, [ and ] are brackets and they are used for the same things as parentheses, y6 is for exponents which is when you use any number or letter and then you put a small sized 1,2, or 3 in the top right corner of the original number to find out if you multiply the LxHxW or LxH or if you just leave it alone, x is for multiplication which is when you multiply 2 numbers together to get the product, -:- is for division which is when you take 2 numbers and you divide the bigger number by the smaller number to get your quotient, + is for addition which is when you add to numbers together to get your sum, - is for subtraction which is when you take 2 numbers and you subtract the smaller number from the bigger number to get your difference.  :)