Some time (with two stresses) means quite a long time.
She has lived in China for quite some time, so she speaks Mandarin quite well.
Sometime refers to an indefinite time, usually in the future; it means one day.
Why don’t we meet for a drink after work sometime next week?
Sometimes is an adverb of frequency, meaning on some occasions or more than once.
Sometimes, in quiet leisurely afternoons, the children lay in the shade of the guava tree in the garden, reading.