To do what?

To check how the example file works:
1. Copy the file into some folder and open it. Probably you have to allow make changes, to run code, etc. Also, it will be best when you save it in xlsm format (the file was created when MS Excel97 was top thing).
2. Into cell B1, enter file extension for file types you want to be displayed (Laiend: ). In cell A2, the folder where the file is copied into, the address of this folder is displayed, and below it, all files with extension you set before, which are found in this folder, are displayed. In C2, D2, ... are all subfolders of folder in A2 displayed, and respectively below them all files with set extension in every of those subfolders are displayed.

To examine how this works in depth:
Open the example file and press Alt + F11 - VBA Project window is activated. There are 3 User Defined Functions (UDF) defined. Those functions are used in formulas on Sheet1, to display folder and files according to extension you did set on Sheet1. Study formulas on Sheet1, and VBA code of UDF's, to understand how this works.