"Unlocked" is a word that's usually used in the content of a mobile telephone connection but that doesn't apply to your device. WiFi doesn't need unlocking - you can connect to any Wi-Fi network you are entitled to use. If a network is secured, you need to ask for the security key and sometimes pay for the time you spend online.
Free Wi-Fi connections are risky because there's no security but if your tablet can "see" one that says its unsecured, connect to check the tablet works. If it doesn't, swipe downwards from the top of the screen and press the Wi-Fi icon to turn the facility on.