Black looking kinda of spot appeared on my upper gum around my tooth , i was told tooth decay ? is that true .

Can't tell..: .. needs to be examined. Decay appears on a tooth, not on your gingiva as you described. have it examined by a dentist.

Staining vs decay: Sometimes staining in the crevices of molars looks like a cavity but is only staining. Ultimately, you should see a dentist for thorough exam to determine where you may have spots or decay. Do not delay.