How do I export my files to mp3 and save them on my computer?

I created a song, but I can’t export it to mp3, it has almost 2 minutes of audio. When I exported it, it was very noisy. I have Wav files. How to transform into midi?

Please post the exported mp3 of the song (or a portion of it) so that we can hear what you mean by noisy. Check also if the noise also occurs if you mixdown to a .wav file.
The screenshot shows that the audio level of the song is very high, as you can see with the red ticks in the upper time axis, which indicate where the song has clipped (i.e. the level became too high). Try lowering the volume using the volume slider in the master channel in the View → Mixer window.

Flavio.

Do you have LAME installed?