You turn it on and you had to type a word or a set of code letters or numbers, whatever, and then that would lead to something else.
你打开电脑必须输入一个单词或一段代码或数字之类的东西,然后才能进入其他操作。
英语百科
Code letters
Code letters were a method of identifying ships before the introduction of modern navigation aids. Later, with the introduction of radio, code letters were also used as radio callsigns.