Alright Punch I'm going to try and explain it without using Tapatalk mobile, because that app is wack as fuck and I hate it.
Assuming you are using the Youtube app, yes? If not, wtf are you doing watching Youtube on mobile without the app? Get the app.
Find the video you want. Not the playlist, no long ass URL full of gibberish. The URL we want looks exactly like the one SD posted above. The cue you are looking for is the = sign, we want that random string of letters/numbers after the equal sign, which is usually the same length as SD's example as seen here: 4E9ydw_aDMg <----this is what you need to find.
If you're on the youtube app, you've found the video you want to share. Underneath the title of the video you should see a row with the upvote/downvote/share/download/save buttons. Hit the Share button and click Copy Link.
Now go to Tapatalk app and write your response. The tags you want are gonna be
[ yt] and
[ /yt] <---remove the spaces in those tags for them to work. You wanna paste the link which is gonna look like this:
https://m.youtube.com/watch?v=4E9ydw_aDMg
And delete everything before and including the equal sign, which leaves you with this:
4E9ydw_aDMg
and then you want to wrap the YT tags around it like so:
[y.t]4E9ydw_aDMg[/y.t]
The periods are inserted in the YT tags so you can visually see the code. Remove the periods and the code will work. I'm not gonna do it for you. Just take that code I posted, remove the periods, and see if it works.