What is the difference between second degree murder and manslaughter?

In People v. Dewberry (1959) 51 Cal.2d 548 (Dewberry), the court held "when the evidence is sufficient to support a finding of guilt of both the offense charged and a lesser included offense, the jury must be instructed that if they entertain a reasonable doubt as to which offense has been committed, they must find the defendant guilty only of the lesser offense." (Id. at p. 555.) In Dewberry, the trial court instructed on murder and manslaughter, explained the two degrees of murder, and told jurors if they entertained a reasonable doubt as to the degree of murder they should give defendant the benefit of the doubt and find him guilty of second degree murder. The court also instructed that if jurors were in doubt as to whether the killing was manslaughter or justifiable homicide, defendant was to be acquitted. But the court did not instruct the jury it should find the defendant guilty of manslaughter if it had a reasonable doubt between second degree murder and manslaughter. This gave the jury the impression the rule requiring a finding of guilt of the lesser offense applied only as between degrees of murder.

Page 4