Hi 3image, check out the Scene Browser topic in the reference section of the help file for some details on the selection filter:
http://moi3d.com/3.0/docs/moi_command_reference11.htm#scenebrowser

> Unfortunately, I have absolutely no clue how to use it. Can you please elaborate?

It can help if you're having difficulty making a selection because of a lot of other things in the way. When you activate a selection filter only objects that match that filter will be targeted for any kind of selection action. So say you want to do a window selection but only have the red curves that are inside the window to be targeted for selection. You can make that happen if you set a filter on Style = Red, and another filter on Type = Curve. Then while those filters are active anything other than red curves will be ignored when you do selections.

There are some more details in the help topic.

- Michael