How to combine two fields in Form to one field from Microsoft Access?

An example is trying to combine first name and last name into fullname from a table thats called employee. What expression do I type in the Control Source? I've typed FullName: [First] & " " & [Last] but it kept saying error.

=[First] & " " & [Last]

Should do it.

To avoid complications with nulls use:

=Nz([First], "") & " " & Nz([Last], "")