Expression Component syntax

Im not sure what to type into the expression next to the U on SrfGrid im trying to make a surface over a grid of points and i copied the definition from someone and they didnt put what to enter into the expression

It’s X+1

Thank you that helped, but it only made it orange and the alter is that the expression did not return a valid value for 40. Do you know what that means? It wont let me bake it.

Check attachment. (6.2 KB)


And how can I learn to write similar mathematical expressions?