Once you have Sven Co-op set up and ready to play you’ll want to set up the Half-Life games you like along with it. First you’ll want to make sure you have those games installed. So install Opposing Force and Blue Shift, run them once and make sure the files are in the SteamApps\common directory because copies will have to be done.
First go to your SteamApps\common\Sven Co-op\svencoop directory. There are two .bat files (assuming you have Windows) to be run. For Opposing Force, click the Install_OpFor_Support.bat file to run it. For Blue Shift it’s Install_bshift_Support.bat. After this you should be able create a Sven Co-op server with the maps of0a0 (Opposing Force) or ba_tram1 (Blue Shift).