Hi,
in KNIME 4.1 you can actually use a single Concatenate node to do this. It now has a little triangle at the bottom left that lets you add more input ports. If you are not on 4.1 yet, you need to use 3 Concatenate nodes, concatenating the tables onto the final result one by one.
If you read the tables from files in a folder, you can also use a List Files node to list the files, followed by a loop that reads them and collects all files using the standard Loop End. An example for that can be found in Workflow Control - Activity II of our KNIME advanced course.
Kind regards
Alexander