That is, you leave the up and down buttons open. Another way: If you want to wear a three button blazer differently, then put the middle button as well as the top button. You must remember that the bottom button should never be closed. Apart from this, you can choose a matching tie according to your formal shirt .
In short, a blazer is a jacket that doesn't form part of a suit, but is considered appropriate for formal wear. There is some disagreement about when the blazer was born. Some believe they were first worn by rowers at Cambridge, who used the jackets as glorified athletic windbreakers.