A simple set of connection rods were recently uploaded that serve as a generic way to connect almost anything to almost anything in any scenario, they were just poles essentially I was looking at them and the instructions? that came with them and thought there is no way in heaven a first timer would be able to get much use from them.
When I first started using RoR a long time ago, as well as many many other open source simulation and physics type programs, there was so little in the way of instructions for how to make what do what, and the RoR user interface and features are still needing improvements to make things simpler (yes I think RoR is great, gee I wish they would focus on the simulators improvement itself rather than the online side of things as much)....
Click, hold, and drag on the part of whatever you wish to connect and move it gently to where you want to connect it to. I then simply observe an arbitrary blue guide line showing two points. One from the part I want connected, the other, where the mouse pointer is.
When it's in place, press the L or o button to connect it to the other item and release the mouse.
Take a page from the old timers at RoR and move very slowly. They know what they are talking about and remember to use different camera angles to precisely line up connections such as semi trailers and other items like dolly plates, because there are other connection points that will cause the simulation to go awry. Alright let me know how you go !
I should also mention that in RoR, some loads will occasionally just refuse to grab. Some loads of other people will transfer through the server, but mostly won't. If you have your "collisions" setting on though, people still mess up a scenario that you have spent hours creating, in the blink of an eye, without so much as a turning around for a sorry. I haven't the time to explain why one of my cranes was able to flawlessly retrieve my friends flipped vehicles from a ravine at one point in time, where as trying to attach a crane to another persons vehicle is, for the most part, fruitless unless you want to see a very unrealistic simulation of a tiny hatchback towing a 120 ton crane effortlessly.