What does Provides do?

[ehud.behar at protonmail.com]

I am trying to understand the effect of the class parameter Provides when inserted into a layout file.

In the Customization manual, it says:
Provides [string] [0 , 1] Whether the class already provides the feature string. A feature is in general the name of a package (e. g. amsmath or makeidx) or a macro (e. g. url or boldsymbol). See Appendix A for the list of features.

What does it mean that a class provides a feature such as amssymb or xcolor? What changes should I see in the preamble of my tex file when including this command? And what about providing a macro. What is the macro "url", for example?
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