Write a couple of your own toy services as practice. Write a one-shot that fires at a particular time during boot, a normal service that would run a daemon and a mount service that fires after its dependencies are loaded (like, say, a bind mount that sets up a directory under /run/foo after the backing filesystem is mounted - I do this to make fast ext4 storage available in some parts of the VFS tree while using a btrfs filesystem for everything else.) You can also write file watcher services that fire after changes to a file or directory, I use one of those to mirror /boot/ to /.boot/ on another filesystem so it’s captured by my system snapshots.
I’d start by reading the docs so you have some ideas about what services can do, then you’ll find uses that you wouldn’t have thought of before.
Offer to help setup the account and show them how to use Mastodon in general.
Also, not necessarily applicable to you but worth keeping in mind: encourage organizations to run Mastodon instances in addition to providing email addresses. If an org is providing email to employees or members for business correspondence they could easily provide Mastodon services as well, this allows members to have public discussions in twitter format without a third party controlling the platform.