If you have not already you need to purchase minecraft and create an account. You can do this here: https://minecraft.net/en-us/ Once you have done so, and installed the game launcher. Open minecraft and login to your account. Hit play, then select multiplayer. Once here hit "Add Server" and type this "play.jailbreakmc.com" into the server IP section. From there you should be good to click and join! Hope to see you playing soon!
are you in 1.13? if so you need to save a new launch option. Close your minecraft and restart it. Before you hit play hit "Launch Options" on the top right ish. Then go down and hit "add new" and change the version to 1.12.2, then go back to the play menu and hit the little up arrow next to play. Change your minecraft to 1.12.2 and you're good to go. The server hasn't quite updated to 1.13 yet!