london euston to kempton park....

i was going to travel via waterloo but have discovered what maybe a better route where you take the train from vauxhall. I'm a bit muddled on where to catch the tube for vauxhall from though is it warren street or euston square/euston, iirc warren street is only 5 minutes walk away from euston???. trainline.com just says euston but it's a different colour line

cheers