Concat is used to concatenate two field values.
For example consider you have table where you have customer info like customer id, Name, Address1, Address2, City, District, State
Now as you can see here in your table you have address spilt in to many fields, if you want to combine them into one, you can use the concat function to concat them one after another.
Hope you understood.For more information you can look in to help.
Please check the Reference Manual or the F1 help (both have the same contents) in order to get information on how a function works, and post when something is not clear and adding as much information as possible regarding your issue. Check this document post on how to use the Community and get the best results.
What Concat() does is to append field (or fields) values. Using the following piece of script.
Names: LOAD * INLINE [ Name Mike John Peter Paul ];
After reloading, creating a new text object with the following expression
Will return the following string
Hope that helps.