Adding the bot C.R.A.I.G. works best, sending waves of units against you and using different paths on some maps. There is a modoption with difficulty settings. Medium and the AI get some extra resources. Hard and it get infinate resources.
You login with springlobby and join the s44 channel by writing:/j #s44
From there you can chat with s44 player online, download the latest Market Garden version and join games.
You can also launch singleplayer games with springlobby.