Create Update Query

I have a number of text files that I have linked to within MS Access. I need
to combine these files into one. All files have the same number of columns
and column names. How do I do this?

I have started to create an Update Query with all the source tables in the
query design window. I have the fields of the destination table in the grid
of the query design window. I do not know what information to put into the
"Update To" grid of the design window.