Dashboard tabs intended for use by a dashboard user must be created as a shared tab. Only non-system tabs can be shared with dashboard users. If you wish to share a system tab with a dashboard user, you will need to make a copy of it and share that copy. Refer to Managing shared tabs.
The process of assigning dashboard tabs to a dashboard user is the same as sharing dashboard tabs with any other user. Refer to Publishing a shared dashboard tab.
You should, however, consider the audience that will be viewing the dashboard tabs. Keep widgets that contain customer or contact names off tabs that will be shown at a public trade show. Best practice is to create the dashboard tab specifically for the audience and purpose, and then share the tab with the individual dashboard user.