Questions. And the answers.

Playing

What happens when nobody plays?: The server sleeps 10 minutes after the last player leaves. You can change that time in the dashboard. A server that sleeps uses no credits.
How long is a wake?: About thirty seconds when a machine is ready. A wake that must first make a machine takes longer.
Does a server that sleeps look offline?: No. Servers are always reachable from your Minecraft server menu, even when they are asleep. You can simply join them to wake them up.
Which address do I get?: One <name>.sculk.app address for each server. Your friends add it in Minecraft like a usual server address. No IPs to remember (or forget).

Is my world safe when the server sleeps?: Yes. The world is in storage. The server writes it there before it stops, and reads it again at the next wake.
Are there backups?: Sculk copies each world every day and keeps the last 7 of those copies. You can also make a backup at any time, and restore one from the dashboard.
Can I use my own world?: Yes. You can upload the world as a zip file in the dashboard.
Can I use mods?: Yes. Easily! You can install mods from the "Mods" screen. Sculk shows Fabric mods for your Minecraft version. If a mod has no build for that version, Sculk says so and installs nothing.

What is a credit?: One credit gives 1 GB of memory for one hour. A 4 GB server uses 4 credits each hour while it is awake.
Do credits expire?: No. Credits on your account stay until a server uses them. Credits from a chip-in stay in the shared pool of that server. Delete the server, and its pool goes back to your account.
What happens when I run out of credits?: The server continues for 30 minutes, then it sleeps. Sculk keeps the world. Add credits, and the next join wakes the server again.
Can my friends pay?: Yes! You can share the cost. Give them the chip-in link for your server. They can add credits to it, and they do not need an account.

Make a server, give the address to your friends,
and enjoy multiplayer Minecraft without the management.