What's different between guten and gute

What’s different between guten and gute

German has three genders for the nouns: male, female an neutral.
These words are adjectives. The adjective is conjugated. The form depends on the gender of the noun.

Der Tag, der Morgen, der Abend = male
Die Nacht = female

I would not worry about this at the very beginning. Learn the expressions in this first lesson as phrases.

“What’s different between guten and gute”

In terms of meaning, there is no difference.