I don't know if you've sorted it out yet but here goes for my teaching skills :).
First of all think of an analogy: you brain in your everyday life. You handle several things at once, some are very obvious and some you don't even realise you're doing. The ones you don;t even realise are basic things your brain handles, like "the calculation" of your balance, eye focus adjustment to what you're looking at, tone of voice, etc.
The obvious is the central task you're performing: reading, memorising, remembering, writing, speaking etc.
It;s the same in computer science where the brain is the CPU. It has background processes and some larger ones if they can be called that, which have been launched by the user or something else ( scheduled to start on a timer etc...).
They are the same, they need CPU time for calculation (like stuff in your head) they need access to peripherals maybe (like you own eyes and mouth inputs and outputs) they read and write and store results - memory or input output relationships through busses - the nervous system.
A process is NOT a program, it is the actual execution of a program.
There may be some connections between processes (shared ressources) and they have more basic components (tasks or threads which may run at the same time in parallel to combine results in the end)
I'm going to stop my physical analogy here to let you ask more if you need more science from me than simple understanding, and others please correct me for some details I may have missed.