Plan first
Decide who it's for, the game mode and whether you need Bedrock players.
Pick a server software
Paper is the default for plugin servers, Purpur adds more options, Fabric suits light mod setups, Forge/NeoForge big modpacks, Velocity links several servers behind one address. ViaVersion lets nearby versions join.
Hardware
A fast single CPU core and enough RAM matter most: 2–4 GB for friends, 6–8 GB for 20–50 players, 10–16 GB+ for big projects and modpacks. Use NVMe storage.
Hosting vs home PC
A home PC works for a few friends (needs port forwarding and exposes your IP). For public servers choose hosting by CPU model, disk type, data-centre location, DDoS protection and backups; a VPS gives more freedom but needs Linux skills.
Launch, domain, plugins
Install the required Java (21+ for modern versions), accept the EULA, tune server.properties. Default ports: 25565 TCP, 19132 UDP for Geyser. Point an A record at the server and add an SRV record for non-default ports. Essentials: LuckPerms, EssentialsX, WorldGuard/WorldEdit, CoreProtect, an auth plugin for offline mode, ViaVersion, Geyser/Floodgate, an anticheat.
Security and backups
No op for others, plugins only from official sources, strong passwords, daily off-site backups that you test. Then add your server and read how to find your first players.