How to join from java
To join the server from java, it is very simple.
Open Minecraft Launcher and Launch minecraft
Click on the Multiplayer button
Click on Add Server
Enter a name for the server, this does not matter to connect and can be whatever you want
In the Server Address field, enter the Server address from the invite email
Click done and now you can join the server by clicking on the servers icon or clicking Join Server on the bottom when you have the server selected.
Have Fun and See you soon in the game!