This is the six eight time signature.
There are six eighth notes in one bar of ) time.
The six eighth notes are divided into two groups of three.
In ) time there are two pulses within each bar, with each beat being a dotted quarter note. (This is different to * and ^ time where each beat is a quarter note).
Accent (play louder) the 1 and 4 count to help establish the two pulses per bar.
The songs "House of the Rising Sun" and "When Johnny Comes Marching Home" are in the key of A minor (Am). The notes used in these songs are from the A minor scale. The key signature for the key of A minor is the same as C major, that is it contains no sharps or flats.
It is common for songs in the key of A minor to contain a G sharp (G#) in its melody as in bar 14 of House of the Rising Sun. For more information on minor scales see Progressive Guitar Method: Theory.
In the early part of the 20th century, guitar manufacturer C.F. Martin released an acoustic guitar with a larger, deeper body than most existing guitars. Around the same time, the British navy launched a battleship that was so big it would fear nothing. It was called "HMS Dreadnought". Martin thought this would be a good name for his new guitar.
The guitar sounded great and the name caught on. Today, the dreadnought is the most commonly used type of acoustic guitar in the world.
Here is an arpeggio style accompaniment for "House of the Rising Sun". Look through the chords and see which ones come from each type of minor scale. Try playing this accompaniment while a friend plays the melody on another guitar. To be a good guitarist, you need to be able to play both the chords and melody of all the songs you learn. This is the basis of rhythm and lead guitar.