The connector must be attached (without glue ...) to one end of the vacuum hose.
When you want to use your vacuum cleaner, just unscrew the filter cap in the swimming pool, and plug the connector on the pipe that goes to the pool filter.
Of course, you will need a power enough filter (sand filter)
This is a version for BestWay swimming pool. For the Intex version, go here : https://www.thingiverse.com/thing:3672591
You can customize it via FreeCad (a free openSource software ! ), as the source file is include.