Are YOU and Atheist?
Yes. There is no evidence for the existence of god(s).

Do YOU believe in Good and Evil?
Yes. In general, people who try to own or hurt other people are evil. Also people who kill animals wantonly. I'm sure there's more, but that will do to go on with. People who are filled with love, light, helpfulness, and justice are usually good.

If not how do YOU define "Moral?"
Moral is right or wrong as defined by a society. Ethical is right or wrong in a more global way. Some of the rules or morality are also ethical, some are ethically neutral.

How do YOU decide what is "moral?"
I decide what is moral by the rules that my society places on our behavior. I decide which of those rules to follow based on whether or not they are ethical or whether or not they apply to me. I decide what is ethical by thinking about it and deciding. It's usually pretty easy. Do no harm. The Golden Rule. Act in ways that the world be better if everyone acted in that way.

Do you have commandments or at least guidelines that you follow or is it all seat of the pants?
Do no harm. The Golden Rule. Act in ways that the world be better if everyone acted in that way.