You don't. Your local instance (open-source.social) pulls down the information from the remote (kbin.social).
For example if you go to open-source.social, select the hamburger menu next to kbin you'll get a drop down with the word magazines, select that.
In the search box type "kbinmeta", you will see one result "kbinmeta@kbin.social". That tells you the magazine is on a remote instance. Select the "kbinmeta@kbin.social"
Someone on open-source.social has already subscribed so the instance already contains posts/comments from kbin.social.
When no one on your instance has subscribed the magazine will be empty. Subscribe and your instance will start displaying posts made from that point