Why can't I login to imessage?

When doing the set up on my MacBook air, the popup asking for my apple id in imessage never came up. Also, when I click on the message tab in the upper left corner to go to system preferences, it doesn't give me the accounts tab. Only general and message tabs. Also, when trying to do the text message forwarding, the needed pin will not pop up on the mac for me to do so.