May be you miss the point of OBS. OBS is an app to capture video stuff (game capture, webcam, etc.) and either stream this live to some streaming service for viewers' immediate consumption. Or instead of streaming, to simply save the captured video stuff on disk.
In this scenario, you don't "save a scene", so it's not clear what you want to accomplish. Instead, you either start streaming, or start recording, and for this you have the two buttons in the lower right corner.
If you already have some raw video footage you want to postprocess and create a new video from it, OBS isn't the right tool for you. In this case, you are searching for a video editor or an nle video editor.
OBS is no video editor, it is a streaming client. You have functions to manipulate the video created by OBS, but that's for life broadcast and not for postprocessing existing stuff.