Download and unzip the file.  Put the lang.custom_download_count.php file in the system/lang/english/ folder and the ext.custom_download_count.php file in the system/extensions/ folder.  Go to ‘Admin- Utilities- Extensions Manager’.  Make sure extensions are enabled- then enable the Custom Download count extension.  You’ll need to go in and select which fields you’d like to hold download count information- so make sure you’ve created a field or two to hold the data.  You select fields on a per-field group basis.

Once you’ve enabled the extension and specified fields to hold download counts, the extension will automatically update the count in the specified custom field every time a file is downloaded via the download lock module.