There will be a popup that will ask you if you want to install Flash.OCX
Make sure the MegaByte drivers are properly installed and that USB support is enabled in OpenFK.
Actionscript 3 support is currently fairly experimental, so expect some bugs.
There are currently no active servers, so you will have to play offline.
This one is a strange one. The way the game scales is not that good, and will result in some glitches which depends on the resolution.
Try using the 'Stretch 4:3' option which will use the original 800x600 resolution.