MLDesigner is shipped with a large selection of demo systems. There are a number of links to demos in the Library View under MLD Examples. When you expand a library item, you see an entry for all the modules contained within the system as well as an entry for the system itself. Observe the different icons for the various elements i.e. Library, System, Module and Primitive.
Many more demos can be found in MLD Libraries/Demos sorted into their categories according to domain. The following example demonstrates the procedure to follow if you want to run a simulation. Once you are familiar with the steps needed to open and run simulations from these libraries, you can explore the Demos.
For demonstration purposes we will choose a system, copy it to a user library, run a simulation, change some parameters, perform another simulation and compare the results.