The patterns ...就是了, ...就行了, ...就可以了
With the colloquial pattern …就是了 
we can emphasize that the action is completed, and that there is nothing more to do.
We should state it at the end of a sentence, usually after an imperative statement.
we can emphasize that the action is completed, and that there is nothing more to do.
We should state it at the end of a sentence, usually after an imperative statement.Examples
你带护照就是了
Take your passport and that's it
nǐ dài hùzhào jiù shì le
请给他五块就是了
Just give him five dollars, please!
qǐng gěi tā wǔ kuài jiù shì le
不用担心，相信我就是了
Don't worry, just trust me
bú yòng dānxīn, xiāngxìn wǒ jiù shì le
The patterns …就行了 and …就可以了 have a similar meaning.
and …就可以了 have a similar meaning. Pay attention
In the pattern …就行了, we can omit 了 and just say …就行.
Examples
牛仔裤和T恤就可以了
Just wearing jeans and a T-shirt will be fine
niúzǎikù hé T-xù jiù kěyǐ le
要是鸡不太大，你把它分成两半就行
If the chicken is not too big, you can simply split it in half
yàoshi jī bú tài dà, nǐ bǎ tā fēnchéng liǎng bàn jiù xíng
来上第一节课就行了
Just come to the first lesson
lái shàng dì yī jié kè jiù xíng le