new to Apple and muCommader

[sofa2011]

Hi, I'm new to Apple and newt to muCommander. Got an Apple now for a week but still have problems gettin used to it after 25 years or so of DOS and Windows. Downloaded nuCommader because I could not realy work with Finder. But I also don't understand muCommander. So I got hunderds of questions. To start: I want to open a picture in my own program of choice from muCommander. But the line " Open with" is grey/supressed so the picture opens in Apples own viewer and that is not what I want. How come? Thanks.

Willem