Sometime means "at an indefinite or unstated time in the future."
Some time means "a period of time."
Sometimes means "occasionally, now and then."
"Why don't you come up sometime and see me?"
(Mae West in She Done Him Wrong, 1933)
"You must give some time to your fellow men. Even if it's a little thing, do something for others--something for which you get no pay but the privilege of doing it."
"I am so clever that sometimes I don't understand a single word of what I am saying."