When you start out, you can either get 3 health potions or get one or two mana potions. You can run out of mana quickly. Once you get to the Frozen Mallet you will be able to take more hits from enemy attacks. You need to horr*** the enemies with your spear shot. The Aegis of Zeonia is good for the blocking and the stun. If you're being overpowered and being pushed back to your tower, the stun can be very helpful. Once you get all 3 of your main skills. The combo that I use is that initiate with the spear shot, jump in with the Aegis of Zeonia, and immediately use Heartseekers Strike, by time this combo is done the spear shot should be done with its' cooldown and you should be able to finish with the Spear Shot. This last shot should either kill the enemy or severely damage them.

Late Game
If you're finished with your build you should be able to be somewhat tanky, and be able to severely damage your enemies with your armor penetration.

You're NOT anywhere capable of being a tank or an insta-kill with this build. You can do significant damage with it though. It it crucial that you are not initiating attacks, but finishing or popping in once the enemies are focused on somebody else. It's important that you use your abilities to benefit you into getting money and kills. Gank, and use your ulti to drop in on team fights. You can really change the battle to your team's benefit.

Overall, don't go rambo into a fight. You're somewhat squishy and prone being focused. Gank other players, and use your Aegis of Zeonia to stun and run away from primary threats. Flash is also a primary escape route in the jungle, or just to get back in the lane. End game, you are powerful and somewhat tanky.