Well I just played my first match alone. I didn't know that there was a game type where you can only pick out of a few heroes, so I accidentally joined one of those. I ended up using Shadow Demon.
I got a lot of kills using his Q move against their Gyrocopter, and SD's ult had a short cooldown so I liked that too. I had no idea how to build him so I just looked around in the shop and bought things that I thought would help. I bought a Mekansm and it saved my life a few times. Overall we lost our lanes pretty horribly because the other team was much better at working together, but I was happy that I seemed to be of equal skill to my fellow newcomers.