You can share a magazine if the publisher has activated "Social Sharing" in the magazine settings.
Learn how to activate Sharing Links here
You can share the preview link or the direct link of the magazine.
To find your magazines link go to "My magazines".
Then click on the little arrow on the right side and choose "View".
You will get the preview link of the magazine:
You can either share the preview link or the direct link you receive by clicking on the "Read" button. The share button in the direct link is at the top right corner of your magazine:
Here is a guide on how to open a magazine on a s specific page