A man-portable air-defense system (or MANPADS for short) is like a really big slingshot that can shoot missiles into the sky. These missiles are meant to hit planes that are flying in the sky, like airplanes or helicopters. They are called "man-portable" because they are small enough for one person to carry around and set up all by themselves, like carrying a backpack.
The way a MANPADS works is kind of like a lock-on machine. The person holding the MANPADS points it at the plane they want to shoot down, and the system locks on to the plane so it knows exactly where to shoot the missile. Then, they press a button and the missile launches into the sky. The missile will fly really fast and go straight towards the plane.
When it hits the plane, the missile will explode and damage it. This can make the plane hard to control or even knock it out of the sky completely. That's why MANPADS are considered very dangerous weapons - they can cause a lot of damage to planes and the people on them.
Because of the potential harm they can cause, many countries have strict rules about who can use MANPADS and how they can be used. Some countries have even gone so far as to ban them altogether. It's important to use MANPADS safely and responsibly, just like with any other powerful tool or weapon.