You need a movie file and a subtitle file in order to use submerge. This step by step guide does not intend to instruct you on how to obtain movies or subtitle files.
1. Open the Movie you wish to add a subtitle to
Find the Movie in the Finder and drag and drop it on the Submerge application symbol. If your movie is already in iTunes you can ctrl-click it and select Show in Finder to find the file. You can also of course choose Open... from the File menu from within Submerge.

2. Select the subtitle file
Now click Choose on the toolbar and select the desired subtitle file. Submerge will handle the most common subtitle file formats like SubRip (.srt) and SubViewer 1 and 2 (.sub) and even the minimalistic format MicroDVD.

Like so...

3. Rendering
Submerge will try to guess the right encoding (the correct character set) for the file and start rendering the subtitles. You can follow the progress on the toolbar.

4. Verify the result
Scroll through the movie and check the result.

5. Correct errors and change settings
If for some reason Submerge could not guess the correct encoding you will see odd characters in the subtitle field. You can change this and other settings in the settings drawer. Give it a try and click Render on the toolbar to see the results.

6. Save or Export the file
If you know that the original movie it in the correct format you can just select save on the file menu. If you need to convert it for say the Apple TV, select export and choose the desired format.

7. Done
If you know that the original movie is in the correct format you can just click Save on the toolbar. If you need to convert it for, say the Apple TV, select Export.. from the File Menu and choose the desired format. When saved/exported you can add it to iTunes or just watch it in your favorite media player like Front Row, VLC or QuickTime Player. Enjoy!
