Latex is formatted math, like you see in the graphing calculator.
Strings are basically text.
Numeric is essentially a number, but not in latex form.
Different functions require different entry types. The ${ } is basically calling in a variable. It needs to be in a compatible form. So, input.latex is pulling in the math formatting instead of just the text.
I don’t always remember what is what, but the errors will usually tell you it expected this or that if you’ve got the wrong type.