You will need to connect your phone first, using USB.
With the USB cable:
adb tcpip 5555
Find out the IP address of your phone
adb shell ip -f inet addr show wlan0
Take note of IP address.
You can now disconnect the USB cable.
If you want to find out the IP address of your phone without connecting it then connect to Wifi tethering and find your "gateway IP".
adb connect xxx.xxx.xxx.xxx:5555
scrcpy
is a nice, free GUI for controlling your device, but there are other options.
scrcpy