Given that you already have alpine with
abuild installed, you need to know that APK signs digitally the APK.
So first you need to create the keys with:
$ abuild-keygen -a
Then, if you have the APKBUILD file in /tmp:
$ cd /tmp && abuild -r
You'll find the built apk according to what is written in
/etc/abuild/abuild.conf, that by default is set to:
In order to install the APK (since as I said is digitally signed), you should copy the public key produced by abuild-keygen in
/etc/apk/keys or alternatively add the argument
apk add $package.