Brand identity is brands logos, typography, colors, packaging, and messaging. It is the visible elements of brands. Brand identity is the brand image which attracts new customers.
Brand guideline is a brand book or style guide, or is a set of rules that explain how your brand works, which are your main brand elements and what is the main goal of your brand. Essentially, it’s a visual document that describes, defines and presents examples of what your brand looks like in various visual media such as print, Internet and broadcast.