I understand it is always a bit hard when you start with new toy (Construct 2). But once you get familiar with what is going on then you gonna love it.
Functions in C2 are really very close to the ones in the "normal" programming. By adding the Function object to the project you simply informing C2 that you gonna use functions in general. It's not a particular function, but just a "schema", consider it like a class maybe or rather "include lib/function". I bet you get the point.
So once you've informed C2 about functions you can create your own functions. Name them as you wish, you can call them whenever you want, send numeric and string params. As String params you can send data structures like Dictionary/arrays as JSON. You can even send "callbacks" in params. Functions also return a value if you need. So it is really very close to the normal function. The only one messy thing is that all functions are global, so you have to deal with this one issue. Oh and return value event doesn't stop the function. Apart of that functions are the essence here as in regular programming.