If you look in your posting bar, there is a vimeo button and a youtube button. Youtube had some recent changes, so it no longer embeds as a regular video. Vimeo as well. If any of your videos in your posts broke, just edit your post and put them between the new youtube or vimeo tags.
You will get some tags. Put the full link to the video in the tags, and that's it. Example:
[ youtube]https://youtu.be/SOME_NUMBER[/youtube ]
The youtube link should be the one from the "share" button on the youtube page. It normally looks like this:
https://youtu.be/SOME_NUMBER
sample:
For other videos, just click the video tags and copy the link in between the tags, like this:
[ vimeo]https://vimeo.com/209831322[/vimeo ]
Sample:
Enjoy!