"The girl asks and the woman answers."
Translation:Flickan frågar och kvinnan svarar.
There's a significant overlap, but flicka stretches a bit lower in age than tjej does, and the opposite goes for tjej, it streches farther up in age.
Flicka means more "girl" in general, tjej on the other hand would mean something like "chick"; hon är en söt tjej = she is a cute girl (like in you're attracted to her)
Sort of, but that doesn't quite catch the difference. As zmzlina said flicka is a younger girl. If you call a 25 year old woman flicka, you sound like somebody's grandmother.
tjej is a little more colloquial but she could basically be any age. (When old people call themselves/each other kille and tjej, others sometimes frown, but it's still done).
Also, only tjej is used to mean girlfriend.