When do botton a suit or un botton a suit?

Hi Antonio,
I just wanted to know when is it correct to wear your suit unbuttoned. Also if are wearing a three button suit, should you always button all three of them? Do you leave the top button undo or the bottom one undo? I know that a suit should always be buttoned if you’re standing in a group, walking or greeting folks. I also know that you normally unbutton your suit when sitting down.