Sanna is, at the very fundamental level, the recognition of an external stimulus. But it is more than that. We not only recognize that a given object is, say, a dog. But some people may be able to categorize it as a bull dog. Thus sanna about a particular object depends on the person.
Same is true for other four senses. When we hear a sound, we recognize what it is, say a bird singing a song. Some may be able to say which bird it is, some may not be. Any smell, taste, or touch works the same way. Without sanna we cannot identify things around us, and also cannot communicate with each other meaningfully.
One of the 31 realms of existence is the “Asanna realm”. There, the beings have no sanna or perception. Thus in principle, those beings are without any awareness. Nothing registers in the mind. If anyone has attained the 7th jhāna, the “Nevasanna Na’sanna“, then that person knows what it is like to born in the Asanna realm.
Next, “Vedana (Feelings)“, ………