Just open it in any text editor.
I need to open the project, not contents of iml file.
Sorry, I understood the question exactly like 'how to see *.iml file contents'.
AFAIK there is no way to start the ide from *.iml. You can create an empty project and import an *.iml into it via Main Menu | File | Import Module
i.e. iml file - not the whole project, and module that's just only be imported into project?
A project file is an *.ipr (old style) or .idea directory