Sharing an item with read-only access is a feature that is available on the Plus and Premium plans. The free plan have access to the standard item share tool, which gives guests full read and write access on a shared item.
To share an item, first click the "Share" button in the upper right when viewing the item.
From here you can select the person you'd like to share the item with, either from your Podio contacts or using their email address, and enter a brief message to let them know what you're sharing.
Check the box at the bottom of this window to enable read-only sharing.
This lets the guest view everything within the item, without giving them access to modify any of the fields there.
Note: If you would like to make your entire app read-only for your workspace members, check out this article for information on that.