Values are concatenated into the field used by the match purpose, with a space inserted between each value. For example, you can select first, middle, last, and suffix columns in your base object. The concatenated fields will look like this (a space follows the last word in the string):

first middle last suffix 

For data containing spaces or null data:

If there are spaces in the data, then the spaces remain and the field is not NULL.
If all the fields are null, then the combined value is null.
If any component on the combined field is null, then no extra space will be added to replace the null.