Hi and welcome!

We have lots of stickied threads on closing for the winter. I'm not expert on blowing out lines, others do it, but the basic idea is a good strong shop vac to blow the line out till bubbles and air come out the return/drain, then, while it's bubbling, plug it, then add pool human-safe anti-freeze to the lines, the same kind used in Rec vehicles water tanks. Absolutely do NOT use automotive antifreeze--it's a deadly poison.