This is a great question, it’s a hard one to answer as there are loads of different things to say!
Every time you try to engineer a solution to something new, you have to start by coming up with a whole bunch of different ideas – even really wacky ones. These are your “concept designs”. Then you have to spend time, using all kinds of design tools that exist – to judge which of your “concept designs” is worth spending time on and might really work.
You also have to think about what your solution is for – so like you said, the important thing is to get Hydrogen into cars, or other vehicles. So we have to think about things like how we connect to the vehicle (we are going to use a hose, a bit like a petrol station), and how to store the hydrogen.
Most of the time is spent solving all those kinds of problems – everyone has different areas of expertise, so I might come up with an idea, but then I need to talk to the people who know about other areas to see if it will really work.
Once we have a good design, then it’s time to start making and testing parts of it to see if they do what you think they will. You can test a whole “prototype” of a design, which is essentially the first one you make to try out and see. Making a prototype teaches you loads about how hard things are to make, or put together, and problems you didn’t expect with how it will work.
The stage we are at now is changing the prototype design to make a solution which is going to be easier to make, put together and better to use, so that we can start to give it to people to really use!