To correct the addle-brained mistakes of young Nobita Nobi, his descendants in the 22nd century sent a crappy robot (that's all they could afford) into the past to serve as his helper and educational guide.
Other characters are Shizuka, a young girl who is the target of Nobita's letchery, and some jock-type character whose name I haven't translated yet. I believe their is a big bully called Gi-an which is based on the English word giant.