Je suis en France = I am in France Je suis dans ma maison = I am inside my house

" dans " is like " in " in english ! ( i think that you don't have problem with "dans" ). But " en " has a lot of uses , the most important one is to express the gerund , example : J'ai mangé la pomme [en] la croquant . Another use of " en " is to express the tool/way , example : Je voyage [en] avion <== in this case , often we use "par"