Turn on your phone and go to the settings app (on most versions of Android can be found by swiping down from the very top of the screen to open the notifications centre, then locating and pressing the cog icon.
On the settings app, locate the option that says “Network & Internet”. Other names may be “WiFi”, “Internet Access”. Press this option.
Press the option “Wi-Fi” to open up a list of the nearby WiFi access points.
Ensure that WiFi is turned on.
Look down the list of WiFi access points that your phone and select the access point with the strongest signal that does not have a padlock symbol next to it, and select that access point (you may need to click “connect”).