One Quick Explanation: When most people think about tuning their guitar, they think from the low E to the high E. The sixth string is tuned to low E, fifth to low A, fourth to low D, third to G, second to B, and first to high E. The high E, closest to the floor, is the first string. The low E, when you count up from the floor, is the sixth string. Frets are the vertical bars you can feel on the guitar neck.
On this site, you may choose one of two methods to learn guitar chords by root note name. Method one uses chord charts that start from the high E (first) string and move towards the low E, or sixth string. Method two uses chord charts that start from the low E (sixth) string and move towards the high E, or first string.