not the first time I was asked, so here goes:
1. from a pc, pick the video you want to share.
2. left click (and swipe) on the address of the youtube vid untill the addy turns blue. now right click and choose "copy link address" from the menu.
3. go to the uer page/post where you want to post the video and open a reply.
4. now.... in the reply box, left click and choose "paste"
5. delete all but "youtube" and the code after the "=" symbol
6. now add at the beginning of "youtube" a "[" symbol and again at the end of the code "]"
7. now.... add any comments or just click "spell check and preview"
and if that looks like the vid you want to post- then hit "post" and you are done.