Start with App Center
Ubuntu’s current help describes App Center as the normal graphical installation route. Search for the intended application, read its publisher/source information and install the supported release. Applications can be offered in different package formats, so note which one you select.
That package choice can affect updates and access to files or removable media. If two copies of the same player appear in the launcher, establish which copy you are opening before changing its settings.
Choose a playback workflow
For an authorised network source, use the chosen application’s own network-input controls. For a library-style television interface, Kodi is a different workflow with add-ons and sources. Do not assume that installing a media player also supplies a subscription or television channels.
Test a known local file first. If local picture and sound work but the network source fails, keep that result: it narrows the problem away from the basic display and audio setup.
Make permissions part of the diagnosis
If the player cannot see a USB drive or a local folder, compare the application’s package permissions and access to that location. A desktop file manager and a sandboxed application do not necessarily have identical access.
Avoid making broad system permission changes just to test a video. Use the package’s supported access controls and the application’s documented file chooser. Keep private playlist files out of a shared public folder.
Keep Ubuntu updated
Use Ubuntu’s ordinary update tools for the operating system and the package source used by the application. A manual file copied from an unknown download page can escape that normal update path. Document the release and package source when seeking help so instructions match the installed system.