Sometimes is a very common adverb that means occasionally or now and then. For instance, Kazuo Ishiguro uses sometimes in The Buried Giant: “She and Beatrice went on conferring in low voices, sometimes glancing towards the crowd, sometimes at Axl.”
Sometimes is an adverb of frequency, which is an adverb describing how often something happens. Some other adverbs of frequency are always, never, usually, and rarely. Sometimes is somewhat special in that it can go at the front, in the middle, or at the end of a sentence. For example, you can say “Sometimes he stays up late,” “He sometimes stays up late,” or “He stays up late sometimes.” The placement of other adverbs of frequency tends to be more restricted.