Right about here, is the bit you want.
http://www.guitarforbeginners.com/tuning.html
When you fret the E string at the fifth fret, (lowest/thickest) you get the note of A. It's the next string played open, (un-fretted) which should sound the same, (A) and so on. The link explains. The fifth string open is usually tuned to A=440 cycles as the reference but initially you just need the strings to be tuned relative to each other.
If it still makes no sense perhaps you should go back to the guitar shop, buy a digital tuner with a visual display and ask them to show you how to use it. They are pretty inexpensive.