Correct spelling, explanation: enough is the correct form since the Old English form genoh ends in a similar way. Due to this origin, the spelling remained with the oh sound at the end. Enought is thus a misspelling.

Definition of enough:
adverb, as much as is necessary; not less that one needs
Five big apples are enough for this pie.
pronoun, if something is enough for a person it means that they don’t want it to go on any longer
Ok, that’s enough. We are going back home.

Incorrect spelling, explanation: this form is incorrect as the word should be spelled without t at the end. It is probably connected to the original Old English genoh, which ends similarly to the correct spelling – enough. Enought is simply a misspelling.