If you're connected via a wired ethernet, just run fw_update(1)
Your em0 device node is for an ethernet device using the em(4) driver. Just dhcp on a single line is acceptable configuration if you just want to device to connect to a LAN and obtain a DHCP lease.
To configure wifi you'll need to configure an /etc/hostname.wpi0
You'll need to configure that appropriately to connect to the wireless access point(s).
https://man.openbsd.org/wpi
https://www.openbsd.org/faq/faq6.html#Wireless