"Life" is a noun. ("He led a successful life.") The noun "lives" is the plural of "life". ("A cat has nine lives.") It is pronounced with a long "i" sound. "Live" is a verb, and the third person singular is "lives". ("He lives alone.") The verb "live" is pronounced with a short "i" sound. "Live" can also be an adjective. ("I caught fish using live bait." "I watched a live broadcast.") The adjective "live" is pronounced with a long "i" sound. And just to be complete, "lifes" is not a real word.

"Lives" is plural form of "Life". Here's another example : plural form of " knife " is " knives "

Extra note: "a" signifies one of something, so it never goes with a plural. "Can the word 'live' be used as a noun?"