Step 1, click the add image button:
Step 2, either paste the image url of the pre-existing meme you want to post (just make sure it's the image file url, you can usually get to it easily on mobile by long pressing an image and selecting "open image in new tab" or on desktop right-click and open image in new tab, then grab the URL from the URL bar). Or, use an image hosting service like imgur or imgbb. Once uploaded, you can long press on the image preview and open it in a new tab, then you have the image file url so you can paste that into the comment:
Now the image is in a new tab, it's just the image file, the URL bar has the url:
Now you can copy/paste those images file urls into the image code in the forums:
You can do the same thing with meme generators like imgflip, just generate your meme and when it gives you a preview of it finished do the long press on it, open in new tab, grab the url to your generated meme.
