It's not clear to me whether you mean you want to list files in your project, or with a picker - you can use a file picker to pick a file directly, or you can use a folder picker to select a folder and then use the 'List contents' action to list all the files in that folder.
It's also not clear to me what you mean by opening the image - perhaps you mean opening in the default associated app, in which case you would use the 'Shell open' action, or show the image in your project, in which case you'd need to read binary data from the chosen file.
Note that if you want to do something like access a folder within the user's Documents folder, you need to use the special picker tag "<documents>", and that only works in desktop exports (Windows/macOS/Linux), and the same goes for the 'Shell open' action.