1. 开 (kāi): This is the most common way to express "open" in the sense of opening something or being open/unlocked.
* Examples:
* 开门 (kāi mén) - to open the door
* 开窗 (kāi chuāng) - to open the window
* 开放 (kāi fàng) - open (as in open to the public)
2. 打开 (dǎ kāi): This means to open something and is used when you want to emphasize the action of opening.
* Examples:
* 打开电视 (dǎ kāi diàn shì) - to turn on the TV
* 打开书 (dǎ kāi shū) - to open a book
Therefore, the best way to spell "open" in Chinese depends on the specific context. If you're talking about the state of being open, use 开 (kāi). If you're talking about the action of opening something, use 打开 (dǎ kāi).