There are various types, but
this is one of them.
It looks like a fly swatter but you don't have to flatten the fly/mosquito/wasp/bug, you zap it. The middle is made of metal (mesh, or in our case thin metal rods). It's got batteries and a button and you electrocute them and then throw the remains out, in the trash or flush them down the drain.
On Amazon.com they are quite expensive, in the Netherlands you can usually find them for €5 to €10 in summer.
It easy because you don't need a wall or surface to flatten them, if your fast enough/insect is slow enough you can hit them in air, usually the remains stick to the swatter, especially if you keep the button down and the electricity going. So no more squished insect sticking to your walls, windows or tables.
If you have a lot of insects bothering you this is a great buy.