My 3 favorite Heroes.
With Kara, he a very strong healer. If you choose the healer build, he can put up impressive numbers and keep his team alive. For the level 20 talent if you are not comfortable landing the palm you can switch to the no CD. Practice it takes time, and requires a knowledge of how bursty your team is. With the DPS build, the build provides crazy chase ability and allows you to follow people to their death. Use SSS when the target is under halfway dead or you are getting low on health. If you see a team mate like Jaina/ETC/Malf ETC trap multiple members of the enemy team use your Q to dive and pop your ULT. With them trapped you will do crazy damage and allow your team to quickly nuke down everyone.

Naz is such a fun character to play. He is so versatile and with practice can destroy the meters. You will want to get very comfortable with your zombie wall. Once you get good at trapping, use your spiders/Ult and watch their health drop. With the level 16 talent, your spiders will chase, so if an enemy is close to death do not chase, let the spiders kill them off. In the early game you will want to build stacks of your level one talent.