That's a great tutorial!
Just to add a little to what Wilorvise said:
The better you understand your subject, the better your figure will be! Gather lots of pictures of the animal you've picked and study them. Proportions (how big each part of the animal is compared to the other parts) and pose (how the animal holds itself) are very important. It can be tempting to focus on details, but if the proportions and pose are not well-done, the whole sculpture will be thrown off.
Even better than pictures is studying the animal in real life. It's a good idea to pick an animal that you can find at a local zoo, park, farm, or (best of all) your own home so you can see it with your own eyes.
If you're going to make lots of figures, eventually you will want to study anatomy (the forms of the bones, muscles, and other internal parts of the animal). It's a big subject and can be intimidating at first, but don't worry, it will become easier as you study it more.
The armature is the "skeleton" of your sculpture. It's very important to make it accurate and sturdy! Soft aluminum wire is available at art supply stores. It's expensive but easy to use. You can use various kinds of wire from the hardware store too, but they tend to be stiffer; they're harder to shape, and it's harder to adjust the sculpture's pose. I could talk about wire for hours, but you probably don't want me to, so I'll just leave it at that.
Polymer clay (including the Sculpey products, Fimo, Cernit, etc.) is probably the best product for a beginner. It's easy to shape, and it stays soft until you bake it (which you can do in a home oven). Once it's baked, you can paint it with acrylic, oil, or other paints.
Air-dry clay and epoxy clay and putty harden automatically, so you only have a limited time to work. That's fine for experienced, confident sculptors, but it can be frustrating for a new sculptor.
Oil clay, wax clay, and modeling wax never harden. This makes them great for practicing and experimenting. But if you want a permanent version of a sculpture made in one of these materials, you have to mold and cast it - a complicated and expensive process!
Traditional, water-based clay (the kind used in pottery, and the main modeling medium used by sculptors for thousands of years) is inexpensive, but it is a little more finicky than other clays. It can be hardened, but only by firing in a kiln (a special, very high temperature oven). Otherwise you can just treat it as a non-hardening clay.
You'll need pliers with a wire-cutting blade to shape your armature wire.
If you use polymer clay, you will need an oven to bake it in (a traditional oven, NOT a microwave). Note: baking polymer clay produces some slightly smelly fumes that will need to be aired out of the oven. For this reason some people don't like to use their kitchen oven for polymer clay. Make sure your family is OK with you using the oven for this before you get started.
You can do most of your sculpting with your fingers. There are lots of specialized sculpting tools you can use, or you can improvise, as Wilorvise suggested. The handles of paintbrushes are handy. So are erasers, popsicle sticks, and all sorts of little bits of wood, plastic, or metal. Most sculptors seem to accumulate dozens of tools, and then mostly use two or three. My most-used tools are this leatherworking tool from Hobby Lobby and some small ribbon tools:
I hope that helps!