Two buttons ① Only the first button (most commonly used and most formal).
(2) No buttons (more relaxed and casual)
③ Fasten them all (use them as little as possible, and untie them after sitting down).
Three buttons? (1) Only the first two digits are deducted (the most common and formal).
(2) Only deduct the middle one (commonly used, regular teaching)
③ No buttons (more relaxed and casual)
(4) Fasten it (use it as little as possible, and untie it after sitting down)
Four buttons (the most casual style, not suitable for very formal occasions)
(1) Only the top three are deducted.
② Only deduct the middle two capsules (recommended)
③ No buttons at all (relaxed and casual)
④ All fastening (use as little as possible, not recommended).
In English, this question is well said: when you buckle this suit, from top to bottom.
The first button is called "sometimes", which means you can button it or not.
The second button is called "always", which means to button it at any time.
The one at the bottom is called "never" and never deducts.
What's the point of buttoning a suit?