When I change something in my application, I usually make project and then run it for debug.
However I want to know when I edit my code and want to build signed apk, is it required to first make it, then generate signed apk or generating singed apk itself include making project in it?
No You don't need to make project when generating signed APK, when you try to generate the signed APK it always builds the project first.
So you can always simply click on generate signed APK after you have tested your app in debug mode.