Videos in Stream first have to be published. Make sure you clicked the publish button on your video before sharing a link or embedding.
After that for people to view your video in Stream these 2 things need to be true.
1. The viewer needs to be licensed for Stream and authenticated with Stream / O365.
2. The viewer needs to be permitted to watch the video based on the permissions set on the video. You can permission a video to be viewable by everyone in you organization or any number of O365 Groups, AD Security Groups, or individual users.
Here is more info on permissions/privacy in Stream: https://docs.microsoft.com/en-us/stream/portal-permissions
