There are three different ways to download files. You can ...
download all files of a transfer at once zipped in one zip file
choose granularly which files you want to download compressed as a zip file
download single files directly
All options have in common that the site must remain open during the entire download process and do not differ in download speed.
1. Downloading all files of a transfer
This option is preselected. Just press the blue "Download all" button to download all files from the transfer as one zip file.
2. Selecting which files to download
Press the arrow next to the "Download all" button and choose "Select files". Then select all the files you want to download and click "Download x files".
3. Downloading a file directly
You can download a single file directly by clicking the icon next to the file name.
Troubleshooting
Problems downloading a transfer? This document is intended to help you. Just contact us in case your problem is not covered.
Download doesn't start or suddenly stops and makes no progress?
This happens when you close the download page. Keep the download page open during the entire download. Cancel the download in your browser and start the download again.
How can I open the download on an iPhone / iPad?
On these platforms, a download following options 1 and 2 is not recognized as a zip archive in Safari. Click the magnifying glass next to the download to open it in Files and unzip it there. Or manually go to the Files app and unzip the download there.
icon next to the file name. 
next to the download to open it in Files and unzip it there. Or manually go to the Files app and unzip the download there.