Cannot download Checksum files

Hello there,
I’m new in Nextcloud an never setup a server in my life, so maybe my question will seem typically newbie…
Trying to setup manualy on Ubuntu 16.04, I downloaded the zip archive. Next step is
Download its corresponding checksum file, e.g. nextcloud-x.y.z.tar.bz2.md5, or nextcloud-x.y.z.tar.bz2.sha256.
What are these files? How to download them? I can find nothing on the installation page.
Thanks for you help :blush:

the checksums allows you to verify the download: