#include <filename> includes filename.inc from includes folder
#include "filename.inc" includes filename.inc from the current directory, it can also have any extension
#include "includes/filename.inc" is the same as #include <filename> but it's better to use the <> method for good practice.
Also, I think this tutorial is too long and too complex for new people, I recommend using a VERRY smaller version without too much unneeded details... like so:
To compile locally you first need to have amxmodx installed.
Compile locally only if the online compiler ("Get plugin" link) outputs errors or plugin developer recommends local compile.
Placing files in the right folders
The plugin soruces (.sma files) go into the amxmodx/scripting folder.
If plugin has additional include (.inc or .inl) files just place them in amxmodx/scripting/include folder.
Compiling into an amxx
To compile just drag and drop the sma file over compiler.exe to compile just that file or double click compiler.exe to compile all sma files in the scripting folder.
Compilation time depends on plugin size, I don't think there's a plugin that takes more than a minute to compile.
Installing compiled plugins
Compiled plugins are placed in amxmodx/scripting/compiled, you need to cut or copy them from there to amxmodx/plugins folder abd after that write their names in plugins.ini, obviously.
Too much details bores or scares the reader :} just my opinion.
There should be an additional part or another tutorial for adding custom includes to your plugin, don't mix them. But I think there is one already :-?