First things first, you will notice that the posting interface has reverted back to the old way of posting or the template used when typing up a word document, so the B, I, U etc, are self-explanatory.
The biggest difference in it is the ability to insert various media without the need to use code or anything like that.
Pictures can be added to a thread by clicking the 'insert image' link and then pasting the url into the box or for those that can be bothered to, you can drag and drop pictures in as easily as that. DRAG AND DROP.
If you want to embed youtube just put the url in the post.
For Twitter, just 'copy link to tweet' (whilst on it) and then paste here.
Alternatively, you can click the 3 dots beside the smile icon to open up a menu where clicking on 'media' will allow videos from many other places to be used. All you have to do here is copy the url of the video you want and then add in there. You can even preview it before you post to make sure but be careful what you upload for obvious reasons including the legal side.