Is this true that touching the vagina with sperms does not cause pregnancy. they have to be inside the vaginal cavity.? because i read online that even if its around it causes pregnancy .how is this possible ?

Sperm are designed to function well in the protected environment of the inner female genital tract. When exposed to the drying effects of air/ outside skin they burn up the meager energy supplies they have & die. I would not expect the situation cited to produce anything. Random posts on the internet are often fairy tales meant to scare people.