American food and the directions to it!!!

ok- i have been to London once that was earlier this month and it was terrifying. Such a huge place and i decided to walk (as no idea where the buses or tubes went) from Kings cross station the the us embassy! Took a long time!!!
Ok so can anyone tell me in simple persons terms (as i have to go down to embassy again in the near future) how would i get say from the embassy to that american food shop is it in convent gardens? Or somewhere around there i think it is.
Not sure if this is a food question or a direction question but hey i just want directions to the food!!!! Unfortunately my food i brought back has been eaten and my nan is terrified to drive down to that AFB to go get her supply (and mine) of yummy food!!! (i know she won't go on the motorway???)

hmm. something tells me its covent gardens... I am SO stupid sometimes!