However, the docs say that the symbol table hash does not contain "my" variables--only dynamic variables.

Let's forget that name and call them "package variables", please.

What is a package variable? Anything that isn't a my variable?

No, Perl also has anonymous variables. A package variable has the form

$Foo::Bar::moo
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This can be abbreviated to

$moo
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in some circumstances.

Well, if we are always told to use 'my' to declare variables, how does a program create package variables?

You seem to be missing the point. Don't use package variables. Always use lexical variables.