Hit the "create" button, select create gif. You can use a YouTube address or if you have a video download can be uploaded to the page for edit. Play around with it, you will figure it out. The videos can only be 20 seconds in the free version of Imgflip. Then to post in comments, from the page of the gif you make, click "show embedded codes". In the BBCode, copy only the part after [img] to [/img]. I hope it helps.
