The structure 一…就… forms a complex sentence and indicates that as soon as one thing happens, then another thing happens immediately afterwards.
We can use this structure in all tenses.
to call as soon as get home
yī dàojiā jiù dǎ diànhuà
If there is only one subject in this type of sentence, we can put it either before “一” or before “就”.
If there are two subjects, we should put the first subject before “一” and put the second subject before “就”.
I'll call you as soon as I get home
wǒ yī dàojiā jiù gěi nǐ dǎ diànhuà
Once the boss explained, I understood
lǎobǎn yī jiěshì, wǒ jiù míngbai le
We often use the preposition 把 with the structure 一…就… .
Once I opened the window, the classroom smelled like flowers
wǒ bǎ chuānghu yì kāi, jiàoshì lǐ jiù yǒu le huā de wèidao
As soon as I put the phone down, it rang immediately
wǒ bǎ shǒujī yí fàng, tā jiù dǐng dǐng zuò shēng le
We also can use the structure 一...就... to express the relationship between the reason and the result. Such sentences mostly are used to express repetitive actions.
We can translate this structure as: “every time there is a certain condition, it will result in a certain event”.