One of the things I did to learn a lot of how this worked was to quote someone who had just done what I was tryin' to do. For example I had the hardest time figurin' out how to post videos till I started copyin' the post that had the results I was tryin' to achieve and postin' it directly above the link and below what the function icon was. When I had the 3 in line for comparison I was able to see the differences between what worked, what the computer software said to do and what the unadulterated direct URL is.
Dependin' on the device you're enjoyin' BFC on and or the current status of the forum's software, (features disabled while troubleshooting) sometimes what's in between the tags doesn't always work. I've gotten so used to typin' it out and just insertin' the appropriate URL between the right tags that I find it quicker that way and other than the basic text commands, no even those, cntrl b for bold, cntrl c for copy I type out instead of usin' the command shortcuts.
The point I was tryin' to make was that just by seein' how somebody else does it where it works and comparin' it to what you do that doesn't work, figure it out by noticing the differences. There used to be many posts on the tech support forum that talked new members through the most common FAQs I haven't looked but I'm pretty sure there's a sticky somewhere on how to deal with almost anything relating to postin' or attachin' a pic or file.