what do I need to do to upload to steam?

A lot of "to" in title.

I exported my project as a Node project and it works when I run it.

If I would submit it to steam greenlight (I assume no game is submitted in the start, only info, images ect), so if my game would be accepted, do I need to add something thirdparty to it?

or do I just submit the app.exe ?

You have to ultimately integrate it with the Steamworks SDK I believe. For Greenlight though yes it is just a video and some images.

You have to ultimately integrate it with the Steamworks SDK I believe

Is this within construct 2 or third party software?

Any tutorials on this?

You don't have to integrate steamworks sdk unless you want to add achievements or other stuff that would require the sdk.

You would just need to upload the files that construct2 exports. When greenlit, they will provide you steps for you to do that you can follow.

since we're in the thread: which kind of export is right for publish on Steam? A windows executable (.exe)?

Walessio: Yes. In the manual article on "Testing and publishing" this is described in the paragraph "Publish to desktop".

thanks Kyatric