There are only 4 parts, the fewer servers to have the easier it is to do theses steps. I.e. on 1 server farms like dev it's pretty easy as all the SQL components are installed hopefully during the initial SQL Server 2012 SP1 install.
Part 1, you need a SP 2013 farm
Part 2, you need to have a database with the SSRS components/functionality install. Now if you are using the same database as your SP database ensure the SSRS components were installed at the initial build. This diagram assumes you have a separate SQL instance which is pretty reasonable.
Part 3, you need to run a core SQL install (only needs the SQL component relating to SSRS) on the SharePoint App/web server. This 1 or more servers containing the SharePoint binaries. This is the step that is new/different and most people don't do.
Part 4, run some Powershell to create the SSRS SSA and hook up the relationship. This is done on any of the SharePoint servers such as your main CA box.
This post couple with the overview should help you understand the components needed for large or automated installs.
http://blog.sharepointsite.co.uk/2013/08/installing-ssrs-2012-on-sp2013-within.html
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Tip: If you need to move your Reporting Services database to another server, you need to manually add the RSexecRole to the new SQL Server.