Learn French: C'est un chien. Il est petit mais très intelligent. - It is a dog. It is small but very intelligent.

This is the main difference between identifying and describing! Use c'est when identifying a noun, like un chien (a dog). Use il est (or elle est) when describing that noun with an adjective, like petit (small) or intelligent.

Why do we use Il for a dog? Doesn't that mean "He"?

Yes, il means "he", but French doesn't have a neutral word for "it". All nouns have a gender, even animals and objects. Because un chien is a masculine noun, we use the masculine pronoun il to refer back to it.

Are the letters "t" at the end of petit and intelligent pronounced?

No, the final "t" in both words is silent. You would only pronounce the "t" if you added an "e" to the end to make the words feminine (petite, intelligente), or if the next word started with a vowel sound.

Intelligent looks exactly like the English word. Is it pronounced the same?

It is spelled the exact same way, but it sounds very different! The "in" and "en" make French nasal sounds, the "g" sounds like the soft "s" in the English word "measure", and the final "t" is completely silent.