OK, I'll try. First some general guidelines, hopefully useful to you and/or other people.
Steps:
1. Select an example file of the type. PNG files should be automatically identified correctly. Do you see "png image" in the file type column of Fluff's file details window?
2. Press F7, or click on the "Props." toolbar button, or right-click over the file details and select Properties. the File Properties dialog appears.
3. In the File Properties dialog box, you should see a button labeled "Type" under the file name toward the right side. Click it, and you should see the "Manage File Types and Hints" dialog box.
4. In the Manage File Types and Hints dialog box, the file type should be pre-selected ("png image ..."). Click the "Associated Apps" button. The "Manage Associations" dialog box appears.
5. In the Manage Associations dialog, you may add or change the application associated with the file type. If you don't see any associated applications, you should click "Add new". A new association entry will be created with the label "Action" and the command-line format "progname %s &". You will need to change these to suit your installation of TinyCore. Maybe change the label "Action" to "View" and the command line specification to "flpicsee %s &" or some other image view that you have installed. Maybe make an entry for "Edit" defined with the command line "mtpaint %s &"
The changes you make are automatically remembered and will be saved when you close Fluff, unless it crashes or is aborted. If you start making changes and want to back out, you may use the "Undo changes" buttons.
The command-line specification may have one "%s" character pair that will be expanded by Fluff with the name or names of the selected file(s). The "&" character allows the launched application to run independently of Fluff, so you can resume doing normal file manager stuff right away, and can even close fluff but keep the launched associated app running. You don't have to follow this exact pattern. I have in the past set up mplayer to "Play" certain media types, but also defined a "Stop" command that had the command-line "killall mplayer".
If your associated command requires multiple references of the filename (more than one repetition of "%s"), you won't be able to do that directly. Maybe it would be best to make a script that accepts one parameter and then repeats it internally as needed.
Let me know if this helps and if you have further questions. If you have a very specific issue, describe what you tried and any info on how it is failing.
The online help file (if installed) covers some of this and more.
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Mike Lockmore