Sometime 1:

1) At an undefined point in time.
John says he'll repair the chair sometime but won't say when.
The electrician says he'll come sometime next week.
I can't remember when the Magna Carta was signed. It was sometime in the Middle Ages.
I really must go to the Louvre sometime. I've lived in Paris for years and never seen it.

Sometime 2:

a) Used as an adjective to describe a situation or position in the past.
Sometime president of Ruritania, Henri Dupont now lives in a semi-detached house in Birmingham.
Sometime gameshow host Donald Trump uses the same techniques and talents as president of the USA.

b) Used as an adjective for something one does occasionally
Chip shop owner and sometime opera singer, Henry Bragge is a founder member of the Scunthorp Musical Centre.
Duval is a sometime presidential advisor and self-appointed expert on social behaviour.

Some time:

A quantity of time:
John says he'll repair the chair when he gets some time.
Picasso lived for some time at Gisors.

Sometimes:

From time to time, when possible:
I sometimes wonder what the world would be like if dinosaurs hadn't died out.
Sometimes, when the pollen count is high, I get hayfever but, oddly enough, not always.
Mary says she can sometimes see the future.