Yes, but not like on a DVD. On a DVD, subtitles are separate from the video, and the viewercan turn them on and off as desired. I don't know of a way to do that in OpenShot.
You can, however, create a text that is always visible in the video.
Put your video clip in track 1, then create titles in track 2 with your text. Don't add a background to your titles. A title without a background will have a transparent background. Putting the title in track 2 will cause it to be an overlay on track 1. You will see the video clip with the text across it.