Genji you can usually follow any PHP setup guide for VPS. Your VPS host might even have some of their own tutorials. Flarum has no special requirements compared to other PHP apps, apart maybe for Composer.
Before starting, I would also suggest doing some reading on server management. It's one thing to install it. Another to keep it secure and updated. If you're not ready to do that, there are plenty of managed servers that work with Flarum.
Once you have PHP+Apache/Nginx+MySQL+Composer running, you should be able to follow the Flarum installation instructions.
For new users I would strongly recommend going for an Ubuntu VPS with Apache.
