Install java sdk then open keytool to create keystore:
keytool -genkey -keystore Your_Keystore_Name.keystore -alias Your_Alias_App -keyalg RSA -keysize 2048 -validity 9999 -v
for local mode signing apk use jarsigner:
jarsigner -sigalg SHA1withRSA -digestalg SHA1 -verbose -keystore Your_Keystore_Name.keystore app-release-unsigned.apk Your_Alias_App
for cocoon just upload your keystore and use the keystore to signing. For complate guide you can check my tutorial here : javanie.com/construct-2-3-build-apk-on-windows-part-2