What is chess strategy?

#1

"I first try and secure/castle my King" ++ Castling is usually good: secures the king and connects the rooks
"Is my understanding of strategy correct?" ++ No, not really. Develop a bishop to b7 and hoping for an attack is no strategy.
"Is this what you call strategy in chess?" ++ No not really. Strategy is about long term plans to exploit the pawn structure. For example in the Queen's Gambit white can play the exchange variation 1 d4 d5 2 c4 e6 3 cxd5 exd5 with the strategy to launch a minority attack with Rc1, b4, a4, b5 aimed at creating a weak black c-pawn that can be won in the endgame.

"a strategy against every and any opening" ++ No, not really. You have to work out a strategy dependent on how your opponent plays.
""learning" chess means learning these openings?" ++ No not at all. Learning chess is not learning openings. It is more learning to recognise tactics and learning endgames: how to win with an extra pawn, how to exploit a pawn structure.