Create a bootable USB flash drive with OS X 10.11 on it, after downloading it on a computer that does have internet access. Then, stick the flash drive into the old Mac, and boot from it (hold Option at startup and select EFI volume).
When it boots, it will prompt you to install OS X. First go into Disk Utility and format the SSD with the "Mac OS Extended (journaled)" format. Then, select the SSD as the destination for your installation.
OP: It would help if we knew what model Mac that you have. I do not know why you need 10.11.6, so I have to guess that it might be because your Mac might be too old to go any higher or it will not support High Sierra. If that is the case then Apple has a article to tell you how to download El Capitan with a link: https://support.apple.com/en-gb/HT206886