1. Explain it simply
着 goes right after the verb: 门开着 means the door is (standing) open, not the action of opening it.
When there is an object, keep the order V着 + object: 他穿着白色的衣服.
To say no, put 没 before the verb: 门没开着. To ask, use V着……没有: 门开着没有？
2. Show examples
门开着呢。
Mén kāizhe ne.
The door is open.
ongoing state
他穿着白色的衣服。
Tā chuānzhe báisè de yīfu.
He is wearing white clothes.
V着 + object
她笑着看我。
Tā xiàozhe kàn wǒ.
She looks at me, smiling.
state during another action
门开着没有？
Mén kāizhe méiyǒu?
Is the door open (or not)?
V着……没有 question
3. Share a tip
着 always sticks to the verb and never moves to the front or after the object. Think of it as a snapshot of a lasting state, not the moment the action happened.