meaning of "He'd better..."

Could you please shed some light upon the omitted part? I know what meaning it bears but what is puzzling me is what it stands for. I’ve heard it’s “had better” but it makes no sense to me. Please clarify.

Thank you!

.
He’d better = he had better.

Had better = would be wiser or more well-advised to; ought to.

‘Had better/best’ is a modal idiom.