For installation, read INSTALL.md.
Running depends on the platform.
On Unix-like systems (OS X only when compiled with the provided Makefile), run
it using bin_unix/client_YOUROS_YOURARCH from either the root directory or
bin_unix.
On OS X, you can use the way above and you can also run it from within the Xcode project (development builds) or you can run the generated app bundle after deploying (the .dmg file also contains gamedata and is ready to ship).
On Windows, execute bin_winYOURARCH\client_win_YOURARCH.exe either from
the root directory or from the directory with the binary.
Samee goes for server, just change "client" to "server". Using the -d2 option to client binary you can get the same dedicated server too (-d1 will start a listenserver).
In case of problems, delete contents of your OF home directory
($HOME/.octaforge on Unix-like operating systems,
Documents\My Games\OctaForge on Windows)
The variable "game" influences what gamescript will be run. In local sessions it's used directly, but when connecting to a server is involved, the server will send the gamescript name to the client (on the server the same variable is used to specify it; modify server-init.cfg appropriately).
Example:
/game drawing.basic
This results in media/scripts/gamescripts/drawing/basic.oct being run.
There is just one map, "test", bundled by default. Use /newmap to create a
new map, just like in Tesseract.
If a problem persists, report it into our issue tracker: https://github.com/OctaForge/OF-Engine/issues