You will notice that on many of our instructions and descriptions we refer to strings by their number (ie 1st string, 2nd string etc...) These numbers refer to the strings in order from thin to thick.
On a typical guitar, the strings are ordered like this.
E=6, A=5, D=4, G=3, B=2 and e=1
If you have an extended range instrument (ie 7 string, 8 string, etc..) then the numbers would continue down below 6, keeping the string numbers for the thinner strings.