If I remember well that cart is on the "Show your FreeCAD project here" topic, and there is even the FcStd file available so you can have a look...
Yes and second sideshow has "credits" underneath and the links takes you here:
Is it a number of parts somehow put together?
Yes there are number of ways to put together parts. In the future as normandc said it will be quite easy and fun task with the help of Assembly
Workbench because you will set some relations between parts and that will be it. There is a video:
Current you can try to make 2 sketches and extrude both (one at a time). Then under property view -> data tab you can control position/rotation... of individual sketch or if you create for example 2 boxes the same applies... Under File you have Merge project... you can use if you have 2 .fcstd files and would like to merge them or you can export solids in other formats and import them in one document and position them accordingly. There are some tools available in FreeCAD that helps to position something precisely or more freely...
You see you have number of ways to assemble something from different objects but the thing currently lacking is to have the ability to do it in a way you would set some relations between objects and the relations would control the assembly
. But don't let that stop you you will get good 3D perception if you will start making assemblies manually anyway and look at this for example:
FreeCAD is more than capable to allow you to build assemblies!