If I understand you right, you need to create a folder with the date of each file and then move the file into it. You can do this with 2 tasks and a loop.
First create a list file task. To ensure grabbing the right files, I like to use a regular expression and make the match as tight as possible to ensure I only grab the right files but you may not have to. For this case I'd use \d{8}_.{6}\.txt for the include file mask which matches filenames starting with 8 digits followed by an underscore followed by 6 characters then a literal dot and "txt". Like I said, you may not need to get this strict. For output settings check to output file name only.
Next create a copy file task. The include file mask will be the current line of the loop (which will loop through the file list from the first task) which we haven't added yet so you'll have to trust me here and enter {LOOP(CurrentValueXLine)}. For the destination folder I build it using the job variable I created for the main folder where the files will be found that I called JobWorkingDir. To this I append the leftmost 8 characters of the filename as found by the loop (using the STRING-LEFT function) and append to the the string "_Folder\" so the while thing looks like this: {JOB(Active|Variable|JobWorkingDir)}\{STRING(Left|{LOOP(CurrentValueXLine)}|8)}_Folder\ The destination filename will be the filename from the loop: {LOOP(CurrentValueXLine)}. If you want to move instead of copy, be sure to check the "Delete source file after copy" box at the bottom.
Now go to the edit job window and add a loop. Start task is the list files task and end task is the copy files task. In the settings tab, check the "For each x in y" and for the value in the "For each row x in" box you'll need to put the stdout for the active task for the list files task: {TASK(Active|StdOut)}.