This post is probably out too late ,as almost all IDEs these days (which support android development) ,probably have an Integrated release signing or debug signing utility/wizard built in, but if somebody is using an old IDE or perhaps want to integrate release in a CI (continuous integration) environment, this tutorial might come in handy.
Basically one has to sign an apk either with a debug key (which is generally present in your .android folder) or create a fresh application-specific keystore, to know more go here