Could you explain the differences between voiced stop, voiceless unaspirated stop, voiceless aspirated stop?

Look at this picture for explaining various mechanics of pronunciation with the vocal cords.

_{Source: wikimedia commons}

I don't understand it much.

Here is what I understood

-voiced stop: your vocal cord vibrates before you release the air

-voiceless unaspirated stop: your vocal cord vibrates right at the time you release the air

-voiceless aspirated stop: your vocal cord vibrates after the time you release the air

Could you explain it using simple easy-to-understand language?

There are two aspects to consider here: voicing and aspiration.
We make sounds by driving air from the lungs, through the larynx, past the vocal cords and on into the vocal tract.
As the air passes through the larynx, it passes between the vocal cords.
If vocal cords are vibrating as the air enters the larynx, or start vibrating before the air has finished passing through, the sound produced is voiced. Whether it will be a vowel or a plosive depends on what happens next.
If the vocal cords are not vibrating as the air passes through the larynx, the sound is unvoiced or voiceless.
As the air leaves the larynx, some part of the vocal tract between the larynx and the lips - including the latter - may momentarily interrupt its passage, partially or completely. If this happens, the resulting sound is called a plosive. So now we can say:
- - vocal cords not vibrating, air blocked: voiceless plosive
- - vocal cords vibrating, air blocked: voiced plosive
For simplicity, I will now deal with stops, which are a type of plosive.
In English, the voiceless stops are p,t,k. Their voiced counterparts are b,d,g.
Aspiration occurs when the stop is accompanied by a little puff of air following immediately after the stop. In English, this occurs with initial voiceless stops, so the p in pin is aspirated: you hear a slight h sound after it. The p in spin or in hat-pin does not have this little puff of air in canonical English speech.
Also in English, voiced stops are never aspirated. They may be in Hindi, though: so bhai with aspiration means brother, and bai without it means old woman. And when voiced stops are aspirated, the h is usually voiced too, whereas in English h is never voiced. So the diagram OP shows us is not very useful for describing English. I suspect it's useful for Chinese languages though.