即: at once, promptly (有错即改, 即将, 即可)
【高16】副词 / adverbs (时间)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
The adverb 即 is the written 就: “at once, right away”. The second action follows the first without delay. You meet it in the pattern V1 + 即 + V2 (有错即改: a mistake, corrected at once) and in everyday words: 即将 (about to), 即刻 (right now), 即可 (it is enough to…, “and that's it”), 随即 (immediately afterwards), 立即 and 当即 (on the spot).
Written and formal register: instructions, notices, the press, set sayings. 即可 is the most frequent in instructions: 填写表格即可 (just fill in the form). In speech you say 就, 马上 or 一……就……
Careful: this 即 is not the 即 “that is” (乃 / 即, 知行合一，即……), which defines instead of saying “at once”.
Examples
填写表格后交给前台即可。
Tiánxiě biǎogé hòu jiāo gěi qiántái jíkě.Fill in the form and hand it to the front desk, and that is all.
列车即将进站，请注意安全。
Lièchē jíjiāng jìn zhàn, qǐng zhùyì ānquán.The train is about to arrive; please mind your safety.
有错即改，不要找借口。
Yǒu cuò jí gǎi, bú yào zhǎo jièkǒu.If you make a mistake, correct it at once; don't look for excuses.
他接到通知，当即赶回了公司。
Tā jiēdào tōngzhī, dāngjí gǎn huí le gōngsī.As soon as he got the notice, he rushed straight back to the company.
会议一结束，他随即前往机场。
Huìyì yì jiéshù, tā suíjí qiánwǎng jīchǎng.The moment the meeting ended, he left for the airport.
在西北，这样的民歌人人张口即来。
Zài Xīběi, zhèyàng de míngē rénrén zhāngkǒu jí lái.In the north-west, everyone can sing songs like this off the cuff.
Common mistakes
✗ 我吃完饭即去了。 → ✓ 我吃完饭就去了。 (in ordinary narration keep 就; 即 belongs to set phrases, instructions and formal texts).
✗ 即将已经开始 → ✓ 即将开始 (即将 looks forward: no 已经).