Question: I am new to creating installers. Before used the Microsoft visual studio deployment package. Now trying inno setup, pretty awesome. 

I saw that Visual studio one wrote some registries when installed.

Do I have to create Registries for my package too? I have a visual c# application and need to create a installer for my company. Main intention is to create a installer that will easily update the old one, but this is a first version of software we are going to release to customers. Much appreciated. I saw tutorials of Registry in internet, but the point of creating is the one that I don't understand.

Answer: 
You don't HAVE to write any registry entries unless your app requires them.
Inno automatically creates the usual entries to allow uninstall from the Add/Remove programs applet.
Inno will also automatically handle [upgrades](http://www.vincenzo.net/isxkb/index.php?title=Upgrades) with no special effort.

If you have previously distributed the app using an MSI package, then you will either need to allow side by side installs (different folders, etc) or uninstall the previous version first. The article above has a sample of how to get the uninstall path.
I'm not sure what you are asking exactly. If you mean how do I write to the Windows Registry, you create a `[Registry]` section in your inno-setup file and add what you need. Here is a [link to the documentation](http://www.jrsoftware.org/ishelp/topic_registrysection.htm).