Ask HN: Guides for first-time smartphone users?

This might sound strange but I am in my mid-twenties and I have never used a smartphone (still rocking an old Sony Ericsson C902 and a Blackberry Pearl). Time, however, has caught up and I just bought a used iPhone SE and a nano-SIM-card should arrive by mail soon.

I am not a laymen when it comes to computers, but are there any websites / resources particularly suited for people like me who are late to the smartphone party?