models directory contains various models
world directory contains various world configurations
screenshots directory contains various screenshots for the world configurations and of some resources
In the all_worlds_name_order.pdf file you can pre-visualize the worlds ordered by name.
To use these worlds you can simply set the path in your launch file/package.
With respect to the models you can copy the needed files (or all of them for simplicity) in the .gazebo/models folder.
Adding worlds directory to the GAZEBO_RESOURCE_PATH environment variable.
To do so, directly use the following command or add the following line to ~/.bashrc:
export GAZEBO_RESOURCE_PATH=$GAZEBO_RESOURCE_PATH:<path to this repo>/worlds
For the models the environment variable of interest is GAZEBO_MODEL_PATH. Again, either locally run or add the following line to the end of ~/.bashrc:
export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:<path to this repo>/models