What does this symbol mean the t shape thing

Can some one me, i’ve been asking for so long

If you shift the linear parent function, f(x)=x, up 13 units, what is the equation of the new function?

The domain of a function can be represented by which one of the following options? o a. a set of output values o b. a set of f(x) values o c. a set of input values o d. a set of both input and output values