Modules: Evo to Revo Conversions

No doubt there is no simple way to answer this, but let's say there is an Evo site that needs to be converted to Revolution. The Evo site is filled with modules of many kinds. However, Revo doesn't use modules.

What is Revo's equivalent of modules? Where do I go to start learning about this? I looked through the documentation but didn't find enough information on it (maybe I don't know the right questions to ask?).

Thanks in advance.

You'll be wanting to have a look at Custom Manager Pages (CMPs):

http://rtfm.modx.com/display/revolution20/Custom+Manager+Pages
http://rtfm.modx.com/display/revolution20/Developing+an+Extra+in+MODX+Revolution

That will give you an idea on how to start building custom pages and functionality within the manager in Revolution. It's heavy going at first and there's a lot to learn - just take your time, read through completely and then try it out yourself one step at a time.