"Sometimes" is an adverb, while "sometime" can be an adverb or an adjective.
"Sometimes" means "occasionally." "I sometimes get the answers right." "Everyone fails sometimes."
"Sometime," as an adverb, means "at some unspecified time (in the future)." "He went to India sometime that I am not aware of." "Sometime soon, I will achieve my goal."
"Sometime," as an adjective, means "former" or "infrequent," but "sometime" is not used as an adjective very often. "Her interest in gardening is a sometime thing. She doesn't do it very often."