打开 (dǎ kāi) means to open or to turn on. 打 is a versatile action verb and 开 means open. Together they describe opening physical things (打开门, open the door; 打开瓶子, open a bottle) and switching on devices (打开电视, turn on the TV; 打开电脑, turn on the computer). The opposite is 关上 (guān shàng, to close/shut) or 关掉 (guān diào, to turn off). Figuratively, 打开心扉 means to open one's heart.