In order to execute code on the EV3, a connection between your computer and the brick has to be set up.
This can be done either via USB or Wi-Fi.
Depending on your operating system, one of the methods described below may work better or worse than others.
To establish and configure any connection, head over to the "Wireless and Networks" sub menu in Brickman.
Please follow the official ev3dev documentation (linked below) carefully in order to get your connection working.

If the brick finds the network
RoboLab Playgroundis connects to it by default. No scan required.
Wireless and Networks and execute Start ScanAccept and wait until the connection is establishedIt is advisable to read the EV3DEV docs first before setting up an USB connection.
All Network Connections and select WiredIPv4 > Change > Load <System> defaultsConnect automaticallyConnect and wait until the connection is established