Hello all, welcome to yet another iteration of our beloved community. Most of what you see should be familiar, at least on the surface. Underneath the paint there's a lot of modernizing that's gone into this build, which should make things more enjoyable for you to interact with our community...
I do it almost the same way as I always did, which might be more steps, but it's what I'm used to.
I post from my phone or iPad - from a desktop it might be different.
I google (for example) Homer Simpson gifs in a separate window.
Then I click "images". All the gifs come up and I scroll thru till I find one I like. I click & hold on the image until it says "copy". I choose copy, then go to the reply box and click on the picture icon, click the little link icon and paste. Click "insert", then hit "reply". Violà!