INTERMEDIATE - GRAMMAR
We use ago to talk about something that happened in the past. We always use it with a period of time (a few minutes ago, many years ago, 10 minutes ago). It is used in past simple sentences.
We use since to talk when something started. It is still happening now. We use since with perfect tenses.
We use for to tak about something that has been happening (or happened) for a period of time. We can use it with perfect tenses or past tenses.