1. Explain it simply
已经 means 'already' and goes right before the verb.
It very often teams up with a sentence-final 了 to confirm the change has taken place.
2. Show examples
我已经吃饭了。
Wǒ yǐjīng chīfàn le.
I've already eaten.
已经 + verb …了
他已经走了。
Tā yǐjīng zǒu le.
He has already left.
已经 signals a change from before
现在已经十点了。
Xiànzài yǐjīng shí diǎn le.
It's already 10 o'clock.
Works with time expressions too
3. Share a tip
已经 usually wants a 了 at the end of the sentence to sound complete - leaving it off can make the sentence feel unfinished.