On its own automatically. The one you push is curation + author rewards only.
To see it happen, don't push the one that asks you to claim it. Write down the number of steem you have in steem power and come back in 3 days. Watch it go up and up. Over the course of a whole year, and without you having to do anything, it increases.
Does anyone have an idea what the APR is equal to then?
https://steemit.com/steem-help/@jerrybanfield/steemit-updates-summarized-from-launch-to-19-0
It's part of the quote I used above, but goes into more detail (which is what you are looking for)
It's not a fixed rate. It's a percentage that can change. In general holding steem power always means your power increases the majority of the time. Read that blog post for more.
Thanks!