Can California actually secede from the United States if it wants to ?

The short answer is, no.

Secession talk in the state that “provided Hillary Clinton with all of her winning margin of 2 million popular votes, and then some, in her losing campaign for president” is nothing more than a flight of fancy:

To dispense with the prospect of California’s seceding from the union: On the gonna-happen scale, it’s a Not. “We’d either have to win the ensuing civil war or have Congress kiss us goodbye,” says Joel D. Aberbach, director of the Center for American Politics and Public Policy at UCLA. “There isn’t a procedure for seceding” in the Constitution. The very notion of the U.S. as a divisible entity was settled by the Civil War.

A constitutional amendment is the longest of long shots. It  must be approved by a two-thirds majority in each house of Congress and ratified by three-fourths of the states (38 of the 50).

And those are the hard facts that a bunch of contrarians choose to ignore.