Basically MIDI does not transmit an audio signal— it transmits "event messages" such as the pitch and intensity of musical notes to play, control signals for parameters such as volume, vibrato and panning, cues, and clock signals to set the tempo. This MIDI file can then be "fed" (for lack of a better term) to any drum, piano, violin, guitar synth. The synth will then read the "event messages" and play the notes accordingly.
For a more detailed explanation of the subject, go here:
Musical Instrument Digital Interface - Wikipedia, the free encyclopedia
It can get a bit complicated to understand at first but for the purposes of answering your question, no you dont need MIDI if you wanted to record your guitar. In fact you dont ever have to use MIDI and depending on the style of music you play, sometimes never will.
I dont know if Ive helped you or just made it more confusing
