Packages
Functions, properties and classes, objects and interfaces can be declared on the "top-level", i.e. directly inside a package:

// file name: example.kt
package foo

fun baz() {}
class Bar {}

If you do not specify any visibility modifier, public is used by default, which means that your declarations will be visible everywhere;
If you mark a declaration private, it will only be visible inside the file containing the declaration;
If you mark it internal, it is visible everywhere in the same module;
protected is not available for top-level declarations.