how do add a gif to my profile?

It's pretty much the same as adding an image: you get the direct URL link of the gif (you can use an image hosting website for that unless it's already provided for you) and use the <img src="insert direct link here"> tag. For example, the code <img src="https://i.postimg.cc/bYtxh6Kp/tumblr-lwzqcqr-Gi-B1r8k88ao1-r1-500-ezgif-com-crop.gif"> makes this gif pop up:

The gif will show up at different parts of your profile depending on which section you place it in (ex: place it in About Me and it'll be there). You can place the tag in-between paragraphs, words, or before the text itself. Basically, the gif will appear wherever you put the tag.

There's different code for if you want a gif to be in a specific place (like under the Mood section or as the background) but I'm just talking about adding gifs, in general. Hope this helps!