I used to have similar shutters - they are widespread across Europe.
They tend to be two kinds - either electric, in which you flick a switch/turn a switch and keep it turned, or manual, where it’s on a tension reel a bit like how a seatbelt works. So you pull down on a strap that is set in a loop on the wall. You need to pull several times to open them fully, but the shutter will be held by the tension reel in the position of the last pull.
You don’t need lots of strength, it’s not heavy (particularly aluminium ones, wooden ones can be a bit heavier). A 3 year old can definitely open them, I have seen it with my own eyes, plenty of times.
If you are trying to open them from the outside (and I have done this myself too, when I locked myself out), the “tension” doesn’t get engaged, so you can lift them up a certain amount (not anywhere close to fully open, but a foot or two), but they won’t stay there, they will drop straight back down again as soon as you let go.