A few more comments to what Ge van Geldorp wrote.
Like in many other open source projects, documentation is not our strongest point...
Nature has no sort of own documentation I am aware of... but it is an excellent project! Many books were written later about it. ROS is just a few picoseconds after the Big Bang... ;)
On the positive side, when you find some docs on how Windows does something (lots of those floating around) then often it will apply to ReactOS too.
Apples are apples! iPods are iPods...
[omissis]
The kernel will initialize itself and the drivers which were loaded by FreeLdr. This should give it access to the disk. It will then proceed to load other drivers. At the end of the boot process it will start the first usermode app, the Session Manager Sub System (SMSS.EXE).
At this point, do not confuse that kind of session with a typical Unix/Windows user session. SM sessions are "emulated operating systems". At present, ReactOS boots only the emulated Win32(tm) session (CSRSS.EXE). We hope it will be able to boot more in the future.
SMSS will load and start the environment subsystems (e.g. CSRSS.EXE, the usermode Win32 subsystem and WIN32K.SYS, it's kernelmode counterpart). It will also start WINLOGON.EXE, the logon process. WinLogon would normally be responsible for logging in users, but since we don't support security yet that's basically stubbed out. WinLogon will then start the users shell.
Recently, in an attempt to clean the design a little to make the SM support easily other OS emulators, loading of WIN32K.SYS and running WINLOGON.EXE were moved in CSRSS.EXE.