There. My 20+ years of experience in software architecture in various fields from games to networking tells me that you now know enough to work out the classes and their relationships in a large software system.
Don't fuss around with "aggregation" or "composition" or whatever. Don't spell out functions (though occasionally I'll jot one below a line to remind myself what the salient feature of the dependency is). And by no means write the class properties, their types, or their access specifiers (public, protected...)—this is way too much detail. A UML diagram is useful in modeling broad object relationships in a system. If you want to work out what properties a class should have, write the damn class. Any software developer worth his salt can figure out the code from a high-level diagram; don't write the code for him. Or do, but then don't call it an architectural diagram.
I know there's a whole culture of software development where architects design code but don't dirty their hands with writing it, then hand it off to underlings who type it up for them, and so on down some kind of techno-bureaucracy Great Chain of Being. Rubbish. Code architecture is a thing and some kind of diagramming is helpful, but UML as such is the sort of busywork and IRS-style hierarchism that marks bloated government jobs, not real productivity or real teamwork.
Give UML a miss and use something very, very simple.