Using Custom Fields for plugin contextualization

Hi folks.

I’ve played with WP in the past – mostly as a simple user – but starting to get into the guts of it now.
Pretty steep learning-curve getting to know the framework, but I’m getting there very slowly. Learning more by trying stuff out & having a series of shall wins.

I see that most/all of the plugins I make use of have “Custom Field” attributes, and it occurs to me that it might actually be useful for something.

What I’ve got are a few posts/entries that I can attach arbitrary attributes to (or simply use the pre-defined ones), and I would like to use some of those in other plug-ins on the posts’ actual pages to provide contextual information.

An example might be to use:
* Events Manager
* WP Google Maps

I’d like to create a GMap entry, and then “do something” with the $CustomFields & $ShortCodes, so that I can associate $Events with the aforementioned $Place – preferably provide a drop-down or auto-complete search/input field (‘$Variables’ for emphasis).
(There are other such plugin integration examples I could cite, but this should be simple enough for illustration-purposes)

I’ve started digging into the source – using the CODEX as reference – but it occurs to me that this might not be an uncommon problem & may already have been solved trivially by the devs.

Can someone please direct me to a good, simple, concise resource I can reference rather than digging in & breaking the underlying code – that’s probably far better crafted than I can expect coming into this now?