It takes a relationship. And there are two ways that same relationship can be used to produce the result you describe. Which method is best depends on details not shared in your posted question, but the following link both describes the two methods and also why you might choose one over the other in a given situation:
Thanks for the quick answer. To clarify here are details:
I have the following values in the lookup table (Current Weather):
ID, Value, Name
I populate the Risk table with the Current Weather::Value field (from the dropdown box)
I need to get the (Current Weather :ID Index) to populate a separate field in the RISK layout (Risk:Current Weather Index) field.
I form the relationship between the two tables, but that's as far as I'm getting...thanks again!
Please read the thread to which I have already provided a link. As I have previously stated, there are two basic methods that can do this and both are discussed in that thread.