Two editions, one world
Minecraft comes in two editions. Java Edition runs on Windows, Mac and Linux PCs. Bedrock Edition runs on phones, tablets, Windows, Xbox, PlayStation and Switch. They look alike, but they speak different network protocols, so out of the box a Bedrock player cannot join a Java server. A crossplay SMP is a Java server with a translator in front of it, so both groups of players end up in the same world, chatting in the same chat and trading in the same economy.
What Geyser does
Geyser is a free, open-source project that translates between the two protocols. A Bedrock player connects to Geyser, Geyser turns their actions into Java packets, and the Java server sees what looks like one more Java player. Everything the server sends back is translated the other way. Geyser can run as a plugin on Paper or Spigot, as a mod on Fabric, or as a standalone proxy in front of a network. Because the server itself stays Java, your plugins and world keep working as before.
What Floodgate does
Java servers normally check that every player owns a Java account. Bedrock players sign in with a Microsoft (Xbox) account instead, so without help they would be turned away. Floodgate is Geyser's companion plugin that lets Bedrock players join with their Microsoft account and no Java account. To stop name clashes, it puts a prefix in front of Bedrock names; by default a player called Steve appears as .Steve. Whitelisting a Bedrock player uses the fwhitelist command instead of the normal whitelist.
Ports: 25565 and 19132
Java Edition connects over TCP and uses port 25565 by default. Bedrock Edition connects over UDP and uses port 19132 by default. Geyser listens for Bedrock players on a UDP port, which you set in its config. TCP and UDP are separate, so on hosts that give you a single port number, Geyser can use the same number as the Java server. Java players can usually leave the port out when it is 25565; Bedrock always has a separate Port box when adding a server.
What works for Bedrock players
Almost everything a survival player does works the same: mining, building, crafting, fighting, chests, villagers, chat and server commands. Plugin menus built from chest inventories work, and some plugins show native Bedrock forms through Floodgate. On a crossplay SMP, Bedrock players take part in the same events, economy and progression as Java players, which is the whole point: friends on a phone can play with friends on a PC.
What is different or does not work
A few Java-only things have no exact Bedrock match, so some blocks, items or particles look slightly different. Combat timing and movement feel different between editions. Java resource packs do not apply to Bedrock players automatically; custom textures and item models need a separate Bedrock pack or extra mappings. Client-side Java mods obviously do not exist on Bedrock. Geyser also has to follow new Bedrock releases, so right after a big Minecraft update there can be a short wait until Geyser catches up.
What about consoles?
Phones, tablets and Windows can add any server by address. Xbox, PlayStation and Switch do not show an Add Server button for custom servers, so console players need a workaround, usually a connection helper that redirects one of the featured server entries. It is a known limitation of console Bedrock, not of the server. ESN keeps a step-by-step console connection guide for the ESN SMP that covers Xbox, PlayStation and Switch.
How to join ESN SMP
ESN SMP is a crossplay survival server with quests, boss fights, custom gear, an economy and seasonal events. On Java Edition, open Multiplayer, choose Add Server and enter play.esnoffical.com. On Bedrock (phone, tablet or Windows), open Play, then Servers, then Add Server, enter play.esnoffical.com as the address and 19132 as the port. On a console, follow the ESN console guide. Questions, events and updates are announced in the ESN Discord.
Set up crossplay on your own server: install
Crossplay needs a Paper or Purpur server (or Fabric with the Fabric builds). Vanilla cannot run plugins. Take a backup first. Download Geyser and Floodgate for Spigot/Paper from the official site, geysermc.org/download, and nothing else. Upload both .jar files to the plugins folder and restart. If your Java server runs an older Minecraft version than current Bedrock, also add ViaVersion so newer clients can connect. Geyser uses some extra memory, so leave a little headroom.
Set up crossplay: configure and test
After the first start, open plugins/Geyser-Spigot/config.yml. Under bedrock, set port to the UDP port Bedrock players should use, and make sure auth-type is floodgate (newer versions set this automatically when Floodgate is installed). Restart, then type plugins in the console and check both Geyser and floodgate are listed. On Bedrock, add the server with your address and that port. To make a Bedrock player an operator, include the prefix, for example op .Steve.
Crossplay on ESN Hosting
On an ESN Minecraft server, your assigned port already accepts Bedrock traffic, so set Geyser's bedrock port to the same number shown in your server's ip:port and keep server-port in server.properties unchanged. Bedrock players then use your address in the Server Address box and your port in the Port box. ESN plans start from $0.50/month; Minecraft needs a plan with at least 1 GB of RAM, and every plan is listed on the panel.
If Bedrock players cannot connect
"Unable to connect to world" usually means the Bedrock port in Geyser's config does not match the port you gave players, or the server was not restarted after saving. "Outdated server" or "Outdated client" means Geyser or the player's game needs updating. Being kicked with an Xbox or login error usually means Floodgate is missing or failed to load. Check the console for red errors on start, update both plugins together, and ask in the ESN Discord with the error text if you are stuck.