Hi

. . . . Is it ipossible to use a audio file from guitar and apply effects in the program  . . . .

You can apply a variety of effects to audio files - please read the installed PDF manual available under Help and watch this tutorial it refers to a previous version however the principles are the same..

. . . . or must it be a midi file? . . . .

No it does not need to be MIDI - and you cannot convert an audio file to MIDI.

They are two different types of files

   - audio eg mp3 is an digitised  'analog' format

   - MIDI is a digital format which contains instructions for how a MIDI synthesizer, whether hardware or software should play the sound.

HTH

John EB