Making love to your guitar, much like making love in general, is something that not everyone can understand or experience. In a figurative sense it is the process of completely breaking down all barriers that are keeping you from playing and becoming one with your instrument. In the same moment of time there can be grinding, wailing, and a complete and utter disregard for the instrument and its well being; however, there can also be the kiss of fingers up and down the fretboard while the other hand caresses the strings.
The form and techniques change from guitarist to guitarist, but the end result is the same: transferring an extreme amount of emotion into a guitar. This emotion is then, hopefully, relayed to other people through the magic of music.
Making love to your guitar is something I do not suggest doing in any manner other than a figurative sense. Electricity can be a foul mistress and steel strings leave nasty rashes.