Meaning:

inform；tell；accuse；announcement；declaration；

Origin:

甲骨文中“告”的字形是上面一个“牛”字，下面一个“口”字，合起来表示祭祀时，人们献上一头牛，并进行祷告的情景，后来，“告”的意思逐渐普通化，泛指“告诉”“表达”和“诉说”。
On ancient oracle bone inscriptions, “告” was composed of “牛” (cow) on top and “口” (mouth) on the bottom, together meaning that people sacrifice a cow and pray in a religious ceremony. Later, the meaning of “告” gradually became more general, and now refers to expressing and telling.

Words:

   告诉 (gàosu): to let others know; inform; to tell

   告示 (gàoshi): notice; official proclamation;bulletin

   告密 (gàomì): to tell on sb.; inform against sb

   告诫 (gàojiè): to dissuade from; admonish

   告别 (gàobié ): to part from; to leave

Examples:

1. 我必须告诫你应谨防危险。

    Wǒ bìxū gàojiè nǐ yīng jǐn fáng wēi xiǎn

    I must caution you to avoid this danger.

2. 你能告诉我到底出了什么事情吗？

    Nǐ néng gàosù wǒ dàodǐ chū le shénme shìqing ma？

    Can you tell me exactly what happened?