How do I ask a women for sex in a polite manner?

you generally get there gradually , i.e. kissing 2nd base, 3d base etc. u don't just ask politely or otherwise.

You don't!!If this woman has an interst in you,she may want the same thing.And is just waiting on you.Here is what you do:Take her out for dinner and a movie,afterwards go back to her place or take her to yours,once the two of you are alone slowly make your advances(don't be too AGGRESSIVE)if she accepts wear protection,if she pushes you away,BETTER luck next time.