One of the more popular forms of cat on the internet, along with cat blogs, stuff on my cat, cats in sinks, cat vlogs, cat podcasts, and cat twitter, is LOLCats, also known as LOL cats, meme cats, cat macros, and I can has cheezburger cats.
For me, it all started with lime cat, but I'm sure the roots go deeper, to some sort of paleolithic cat wall carving.
Step 1: Acquire Cat Images
Step 2: Find the Right Picture
It might take some time, but you need to find something that makes you say, "Damn. That's some funny-ass cat right there."
Step 3: Edit Your Cat
Step 4: Caption Your Cat
Well, there's a great analysis of LOLCat speak, here, but this is why the picture has to inspire you.
LOLCat vocabulary does have certain highly frequent memes and words, including: "I'M", "IN", "UR" (your), "INVISIBLE", "HAS" (have), "MAH" (my), "HAI", (hi) and "BUCKET". These are then combined into forms like "IM IN UR FRIDGE, EATING UR FOODS", or "INVISIBLE BICYCLE."
In this case, I saw jumping. I saw bright colors. I saw an attack. I saw.... INVISIBLE PINATA!
Generally LOLCats type in white and in all caps, but there's no fixed rule.