电脑 (diàn nǎo) is the everyday word for 'computer' in Chinese — it's what you call a personal computer, laptop, or desktop in daily conversation. 计算机 (jì suàn jī) is a more formal or technical term, often used for the concept of computing or a computer as a machine; it's also the word for 'calculator' in Taiwan. For everyday use, stick with 电脑.