Learn Hardcore French: Il a un chat et un chien.

In French, chat (cat) is a masculine noun, so it takes un. If it were feminine, like une souris (a mouse), you would use une. Therefore, un chat is correct for a male cat (or simply the word for "cat" in general).

Is the "t" in chat pronounced?

No, in standard French, you do not pronounce the final "t" in words like chat. It's pronounced roughly like sha.

Why do we use et and not est?

Et means and, while est is the third-person singular form of être (to be), meaning is. In this sentence, Il a un chat et un chien, the correct conjunction to connect the two objects is et (and).

Does il a mean both "he has" and "it has"?

Il can mean he or it (when referring to a masculine noun). Il a literally translates to he has, but in some contexts (such as talking about a masculine noun), it can function as it has. However, in everyday usage, il usually means he.