That video is awesome seriously. I got the fan to work using a computer power supply! I just need to cut the wires and solder them together. I only need the peltier and a decent heatsink cooler and i'm good to go

what does it mean : cut on?..........why did he bridged the pins at the 24 pin connector? what is that for?
I think "cut on" in the video means the electricity running through the powersupply. So when he said to bridge the pins in the 24pin connector to make it cut on, he means you need to do that so the fan and peltier will get electricity. This is only if you have a powersupply that doesn't have a switch. If you have a powersupply that has a switch then you no longer need to do that bridging in the 24pin.
and how can it be set on a timer? does it mean that at a specific time each day , it will start and after a few or many hours it will stop aswell ?
The timer is simple. Just plug the power supply to one of these and set your the timer:

- Electronic timer
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The timer that i can get in our local hardware store can be programmed to the minute and it is possible to switch them on and off upto 7 times a day. But if you want don't want the hassle of timing everything just buy one of those thermostat.
A good one that i'm looking to buy is this:
Temperature Controller of Thermoelectric Cooler PeltierIt'll keep the temperature constant throughout the day!
For a electronic noobie like me i had to learn via trial and error. I was like "am i ready to get electricuted" everytime i splice wires haha.
at the beginning , when he connected the wires with the heatsink fan -----you have to take(connect) only one of the yellow wires, and a black one too?
Nothim, the heatsink fan must be connected to the (yellow or red) and black wire of the powersupply. You could just insert the bare wire in the pin and it'll work. I did it last night and fooled around with the wiring. I think i've short circuited the power supply after i place both wires in the yellow wire slot.
if you use this device in a humidity room , for cooling the environement, you just have to leave the device inside there for cooling the air, but what is going to happen with the hot air from the heatsink?
is it not going to stay there aswell 'neutralising' the cold air?
do you have to leave only the peltier cooler side inside and the rest ( heatsink and fan) outside the humidity tent?
Hope this brings light to you:

- Peltier10.jpg (35.36 KiB) Viewed 10209 times
The idea is to have two heatsinks to make the cooler efficient. One heatsink is for cold side(inside the box) the other heatsink (hot side) is outside the box.
how many of this devices (peltier, heatsink, fan, power supply) do you need in order to cool a one cubic meter space if outside are around 35 celsius or more ?
Ideally you only need one peltier and powersupply. two heatsinkfan for hot and cold.
For a cubic meter you need a peltier chip that has a large wattage. The higher the wattage the stronger the cooling. just keep in mind that the pc power supply can only supply 12v and 250watt peltier chip is usually 15v. You won't be able to maximize the peltier chip.
I bought a 130w chip, i'll let you know how it goes.