What happens next?

How to vacuum your pool and backwash the filter
Turn off skimmers as noted on pipes.
Start by attaching the vacuum hose to the vacuum head.
Flood hose with water before placing adapter in skimmer to avoid loss of prime.
Some skimmers require you to remove the basket before you can attach the hose, so be sure to do this if necessary. Holding one end of the vacuum line over the return port is a good way to bleed out the air trapped in the line.