Insect hotels serve as a residence and shelter for various types of insects, but are mainly used by solitary / wild bees and butterflies.
They usually consist of different parts that provide shelter for a particular insect, but some are specifically made for one species.
Wild bees in particular are enormously helped by placing an insect hotel, because they do not find enough nesting cavities in the remaining forests.
They find the hotel automatically and after a few years you can have up to hundreds of wild bees in it. They don't sting either, so it's safe for children!
The best location to place the hotel is in the sun and facing east or south, eventually also west.