How do I set up multisite on Digitalocean?

Yes it’s easy.
You should start reading Digitalocean’s documentation, for newb it will take few while to understand the whole scenario but you if have past experienced with managing VPS server then i believe it will be fun for you.
This documentation may help you : https://www.digitalocean.com/community/tutorials/how-to-set-up-multiple-wordpress-sites-using-multisite