Kissing hands is a way to show respect to someone who is older, wiser or more important than you. It's a very old-fashioned tradition that people used to do a long time ago, but not so much anymore.
So, imagine that you meet a very important person, like a king or queen or maybe even your grandma who is very wise and you really look up to. Instead of just saying hello, you can take their hand gently and put it close to your face, then give it a little kiss. This shows that you think they are special and worth treating with extra kindness and respect.
It's kind of like a special way of saying "hello" that makes the other person feel really good and important. But, it's important to remember that not everyone likes having their hand kissed, so it's always a good idea to ask or watch to see what other people are doing before you try it yourself!