Some prerequisite information for installing Devuan
Writing an image to bootable media
All Devuan and Debian images are hyrbid ISO’s and may be written to a USB drive using dd.
dd if=filename.iso of=/dev/sdX
Substitute X for the disk you want to write to.
Or you can write the image to a CD or DVD.
wodim dev=/dev/sr0 -eject filename.iso
Configuring the BIOS to boot from a CD or USB drive
Whilst it is not possible to cover this fully (every BIOS is different) some general tips can be given.
After powering on to enter your bios the keys F2 or DEL are usually used.
Once you have entered your BIOS you just need to find and change the boot order of drives so that USB comes first, DVD/CD-ROM comes second and the hard disk comes third.
Alternatively most modern BIOSes will allow you to override the boot oder when booting. This is often done by pressing a key before the post screen dissapears, or in the case you have a quick boot before the screen turns on. Often this key will be the F8 or F12 key.
The friends of Devuan wiki has an install guide you can follow for installing from your bootable media.