The ‾ operator gives the negative of the value immediately following it. It's not to be confused with the - operator, which subtracts two numbers — while on paper you'd generally use the same symbol for -2 and 4-2, the calculator has two different symbols, and negation is represented by the slightly shorter and higher dash.
You can also use ‾ to negate lists and matrices, which will negate each element, as expected.
:1+‾1 0 :‾(x-1) ‾x+1 :‾[1,2;3,4] [‾1 ‾2] [‾3 ‾4]
Other pages on this site will use - to mean both subtraction and negation, where it isn't confusing.