I'm not 100% clear, do you mean use two fields to lookup based on 2 values in a lookup table?
AS an example say you had a list of first names and surnames, and you want to look up their phone number from a lookup table. You can't lookup based on first name because there are, say 2 pauls, so you need to lookup based on both first name and surname?
What I tend to do in these situations is to created a "contcatenated key" to lookup.
So in my lookup table I'll add a column to the left with a formula which combines both columns (I usually add something in the middle,like a dash not sure why but I do!)
So if column A is first name, column B is surname, in column C add:
which will give you e.g.
once that is in your lookup table, when you are doing the lookup you simply do a similar concatenation e.g.