Open strings are the unfretted strings of the guitar - no fretboard fingering required! They are the strings that are played without pressing down on any frets.
In standard tuning; The open strings of a guitar are tuned to the notes E, A, D, G, B, and E.
Open strings are used as the foundation for tuning the guitar and are often used as a reference point for tuning the other strings.
A handy way to remember the names of the open strings is to use a mnemonic. A popular mnemonic is 'Eddie Ate Dynamite, Good Bye Eddie'.
Below is a list of shapes to learn to get you started:
E Open String (Low)
Abbr.: E Notes: E
A Open String
Abbr.: A Notes: A
D Open String
Abbr.: D Notes: D
G Open String
Abbr.: G Notes: G
B Open String
Abbr.: B Notes: B
E Open String (High)
Abbr.: E Notes: E