You should have checked out (subversion checkout URLs here):
trunk/libgdiplus
This is a library used by System.Drawing.
trunk/mono
This is what we call the Mono runtime. Contains mainly C source code. Under this directory you can find:
- data/: a few configuration files for different version (1.x, 2.x,...).
- msvc*/: Visual Studio solution files to build the Mono runtime.
- libgc/: the Boehm Garbage Collector sources.
- mono/: Mono runtime sources.
- mini/: JIT source code
- metadata/: these are almost all the functions used by the Mono runtime (marshaling, thread pool, socket I/O, file I/O, console I/O, application domains, GC, performance counters,...). It's more or less one C file each.
- util: miscellaneous functions.
- io-layer/: Win32 I/O emulation functions.
trunk/mcs
This is where the C# compiler, the class libraries, class libraries tests and other tools are.
class/ : One folder per assembly. Each of them contains the source code for each assembly split in directories with the namespace name (ie, System/System.Configuration and so on) and usually a Test directory too. The only naming exception is mscorlib whose corresponding folder is called corlib.
For example, if you want to see the source code for System.Net.HttpWebRequest, which is in the System.dll assembly, you go to trunk/mcs/class/System/System.Net and there shoould be a file named HttpWebRequest.cs containing the code you're looking for.
mcs/: the sources for the C# compilers (mcs, gmcs, smcs, dmcs...)
- tools/: these are a bunch of tools used for development (sn, wsdl,...), documentation (monodoc), etc. Most of the tools names match the MS ones.
There are a lot more directories around, but those are where you should look for the C and C# code. Also, I suggested trunk for the checkout, since you will get the most up-to-date sources that way.
Update: Mono resides now in github and mcs has been integrated into the mono repository.
