That's what you asked for.
ThisThing = OtherThing is a Boolean expression with a result value of 1; or 0.
If ( Get ( LastMessageChoice )=1 ; GetField ( HR || Individual Notes::Start Date AL ) )
I tried this too but it still show 0
Tried how? That expression makes no sense. What is the whole script? Why use getField? Looks like some very basic training on how to design with Filemaker is in order here.
"how do I copy the content of a field and store it in a field in a portal?"
Option 1: Don't do it. Instead, enter the data direcrly into fields of the portal row. There are number of options for how you can do that.
Option 2: Use MagicKey. You can web search this term to find out more.
Option 3: Use global fields for entering the data and the following script:
Set variable [$ID ; Value: layoutTO::primaryKey ]
Go To Layout ["PortalTO" (PortalTO) ]
SetField [PortalTO::ForeignKey ; $ID ]
Set Field [PortalTO::Field ; Globals::GlobalField ]
with New Window, you can hide it by positioning it off the edge of the monitor.