So example of that wud be....if you saw this..
----0---- <---thin string (High E)
----0----
----1----
----2----
----2----
----0---- <---fat string (Low E)
1st the Fat string, you dont hold any fret's, cause it indicates 0 on that line, meaning its an Open string. The 2nd string (A) you would put your finger on the 2nd Fret, (the 2nd space up the neck inbetween the 2 metal bars or 1 before the 1st dot on the neck) so you hold the A string down inbetween the 2nd Fret. the same for the 3rd string (D) 1st fret for the 4th String (G) open for the 5th and 6th strings (B,E) that makes an Emajor Chord.
Hope that wasnt too elaborate :o