Final answer:
To install apps from unknown sources on a Firestick, enable the 'Apps from Unknown Sources' and 'ADB Debugging' options in the 'Developer Options' section of the Firestick settings. Ensure to only use trusted sources to minimize security risks.
Step-by-step explanation:
To install unknown sources on a Firestick, you need to enable the option that allows the installation of apps from outside the Amazon Appstore. Here's how you can do this:
Go to the main screen of your Firestick and select 'Settings.'
Scroll to and select 'My Fire TV' or 'Device' (depending on your version of Firestick).
Choose 'Developer Options.'
Switch on 'Apps from Unknown Sources' and 'ADB Debugging' if necessary.
A warning message will appear regarding the risks of installing unknown apps. Read it and then select 'Turn On' if you wish to proceed.
After enabling this setting, your Firestick will be able to install apps from sources other than the Amazon Appstore. Remember to only download apps from trusted sources to reduce the risk of malware or other security issues.