Vacuum cleaners use air pump to suck air and everything else that comes in the way of its mouth. The dirt is collected using a filter or a cyclone and will be disposed of later.
There is always a bag to collect the dust, but new vacuum cleaners use exhaust filtration, a method that is called Cyclonic Separation spins the intake air so fast that dust is forced out of the air and tumble into a storage bin. Like a centrifuge. Using this storage bin, there is no need to use a bag and it is healthier.
A Bagless Upright Vacuum Cleaner is even more power. Bagless Upright Vacuum Cleaner can offer you more formidability in vacuuming as it would not take up so much space and the vacuum cleaner is powerful and uses cyclonic separation as well.