There are several ROS interfaces available for CoppeliaSim. Each one offers a specific behaviour, feature, or a way to operate:
The ROS Interface: the ROS Interface duplicates the C/C++ ROS API with a good fidelity. This makes it the ideal choice for very flexible communication via ROS, but might require a little bit more insight on the various messages and the way ROS operates. The interface comes in two flavors: the ROS Interface, and the ROS 2 Interface.
The ROS plugin skeleton: this represents a skeleton project that can be used to create a new ROS plugin for CoppeliaSim. Make sure to first have a look at the ROS Interface source code before attempting to edit this project.
ROS interfaces developed by others: those are not directly supported by us. For instance, the CoppeliaSim ROS bridge.
All ROS interfaces can normally operate side-by-side, but we highly recommend you to first try your hands on the ROS Interface, since this is the most flexible and natural approach. The packages to the first two above listed ROS interfaces are located here and here. Use the catkin tools to build those packages, otherwise you might run into difficulties.
Also have a look at the ROS tutorial and the external controller tutorial.