Flood and deluge have almost exactly the same meaning. Both words describe the disaster that occurs when water flows over its usual barriers, such as when a river or lake gets too high and the water flows over the land, in a possibly destructive way.
When flood and deluge are nouns, they have exactly the same meaning, except that deluge may sound like a larger flood—although this is only a connotation:
The flood after the rainstorm was not as bad as the Biblical deluge.
As verbs, flood and deluge are slightly different:
Water flooded/deluged the community. (interchangeable)
The river flooded/*deluged. (only flood can be used this way)
You cannot use deluge as a verb without an object, making it a transitive verb.