What gets saved in an iphone backup?

I want to backup my iphone onto my computer and i was wondering what is saved and what is not saved. And what happens when i restore my backup? Will it be exactly like my old phone? Will it save everything? Examples: contacts, photos, passwords, etc. I specifically want to know if my texts will all be saved. I've had some important conversations that i don't want to be deleted.

If done to a computer, everything is. A full backup.