Here's my analysis, take it as you will…though I'm not sure this was the correct category to post in.
The Arrangement: This is clearly not a complete song (I hope, right?). At bare minimum, I would add the obvious drums and bass guitar. The drums could be samples if done well, but it absolutely needs that backbone. The bass will obviously help drive this rhythm and fill it out. A second guitar part (or more if you wanna get crazy) would probably add some spice too. Maybe something with some lead licks. Also, if you've got access to a synth or software, it wouldn't hurt to try layering some stuff on top…who knows, it may sound cool (it may sound like shit).
The song: It's not bad, I feel that it needs to have some sort of break from those same chords, but it's really hard to tell with how stripped down the recording is. It seems like it would have adequate dynamics if it weren't just a guitar and voice. I have no idea what the lyrics are; I don't speak Portuguese
But, it seems like it could be a better song with a little less repetition.
The Singing: This part could definitely get better. At certain points in the song (in certain ranges) it sounds ok, but it seems like he struggles to hit some of the higher notes. It also seems like he cannot keep up with the quicker movements in the melody…he's essentially writing checks his vocal chords can't cash. This is not to say that practice would not help…in fact, I think he certainly has potential. For now, I would either check out some YouTube vocal lessons or write songs that stay within that easier range.
