Here we choose webots_2020b-rev1_amd64.deb. Newer versions are also supported.

https://github.com/cyberbotics/webots/releases/

After fetching the .deb file

step 1 Move webots_2020b-rev1_amd64.deb to home directory step 2 Open a new terminal and run

sudo apt install ./webots_2020b-rev1_amd64.deb

step 3 Set the environment variable: run

export WEBOTS_HOME=/usr/local/webots/

step 4 Start ugly_car

roslaunch webots_ros ugly_car.launch