How to play the smooth sound of the lower arc in the guitar score of Hotel California?

This is a hyphen. It means that the last sound extends to the next sound, which is equal to the duration of the last sound with two sounds. Take the picture as an example. After playing the three strings and seven frets once, hold it down and extend it to the next note, so that this score can also be regarded as the 7 behind the arc. Legacy symbols like this are usually preceded and followed by sounds, and the following can be omitted.