To play or copy media to/from other devices (e.g., computer, TV, etc.), they must be connected to the same Wi-Fi network and may need to be configured for sharing. Contact the equipment manufacturer for assistance.
For assistance setting up a Google® Chromecast™ device, refer to this page.
Some apps (e.g., YouTube, Netflix, etc.) support displaying the app contents on a remote display. Within the app, tap the Cast icon then select the desired display from the list.