Why is my kitten scared of everyone?

I got my kitten a few hours ago and he is 3 months old and not from a shelter. Anyway i got him a few hours ago and all he has been doing is hiding and hissing at everyone. When we got him he was an inside cat that has always been with his mom in a small room and never been outside. And wen we brought him home he ran away and hid in our garage i got him and held him but he just kept on meowing and meowing and wanting to break loose and wen i did he ran far away and i had to chase him we live in the country by the way and we got this cat as a companion for are bigger cat and they seem to be getting along smoothly but for everyone else she just runs away. By the way what should i feed him please answer.