The word "kind" means "nice" and "not cruel". However, you don't hear it used much in daily conversation. People do use "kind" in some set expressions, like:

How kind of you.

And it's OK to tell someone to "be kind to ___":

Be kind to animals.

However, it sounds a little strange to describe someone as being "kind" in everyday speech. There are a few reasons for that:

1. "Kind" is a slightly formal word. It's used mostly in novels, children's books, and so on.
2. You usually describe someone as "kind" when they have more power or a higher social position. So, for example, a queen can be "kind" to her subjects, and a man can be "kind" to his pet. In earlier times, before there was equality between men and women, you could talk about a husband being "kind" to his wife.