"I was at home" implies that you were at home, once, but not now. "I've been at home" implies that you were at home *until* now. (or implies that you were at home during a time period between then and now) "I was at home.....the other day." or "I was at home...yesterday." "I've (I have) been at home....until now." or "I've been at home.....since yesterday." or "I've been at home....between yesterday and today." Hope this helps!