To reduce the size of files or to package a group of files into one download, compression is used. A common format you may have heard of is ZIP.
If you download a ZIP file from Putkeep you will need to find it in your downloads then right click and choose 'Extract All'. The process may be slightly different dependent on whether you are using Windows, Mac OS, Linux or mobile.
Most are able to open ZIP files without extracting so you can see inside which can cause you to think they are okay to use with extraction but this is incorrect.
You need to extract files from a ZIP file before using them. It would also be a good idea to move the UNZIPPED folder/file into your Documents in case your Downloads are not backed up.