刚
gāng
The 'just now' where the door is still swinging
The picture A door that has only just closed, still swinging gently back and forth. 刚 is a trace still swinging; 马上 is a thing that has not arrived yet.
Where the picture shows up in 刚
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the just-now on your shoulder
我刚到公司，还没换衣服。
wǒ gāng dào gōng sī, hái méi huàn yī fu
I just got to the office — I have not even changed yet.
A bag strap still hooked over one shoulder while you stand catching your breath
A following 还没 adds what you have not managed to do yet.
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the just-now in a meeting room
会议刚开始，你快进来。
huì yì gāng kāi shǐ, nǐ kuài jìn lái
The meeting just started, come in quickly.
A handout open at its first page while a hand waves toward the door
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the just-now at an empty seat
他刚出去，您等一下。
tā gāng chū qù, nín děng yí xià
He just stepped out, please wait a moment.
A coat still on the chair and steam still rising from the cup on the desk
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the just-now on your head
我刚起床，头还有点晕。
wǒ gāng qǐ chuáng, tóu hái yǒu diǎn yūn
I just got up, my head is still foggy.
Flattened hair untouched, a palm rubbing slow circles on the forehead
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the just-now on a sachet
这个药刚吃，别再吃了。
zhè ge yào gāng chī, bié zài chī le
You just took this medicine, do not take any more.
A torn sachet beside a glass of water drunk half down
To name the moment itself you use the noun 刚才 instead.
All of it in one picture
刚 is a door still swinging. Put that motion on your own shoulder and it is an arrival so fresh the bag is not down yet; put it in a meeting room and it is a start fresh enough to walk in on. Put it on someone's chair and he has only just stepped out; put it on your head and you are barely awake; put it on a sachet of medicine and it becomes a warning not to take another. Something has passed just now, and you can still see its wake.