To join you will need the FTB Legacy launcher found here
Or you can use the curse launcher found here
Click on Create Profile in the lower right hand (If not already done)
Click on the FTB Modpacks tab and click on FTB Infinity (Click on Infinity Skyblock for Skyblock)
Install the pack (You don't need to add any additional mods)
Click Launch to launch FTB Infinity

We are currently running the version listed here

Server ip:

North America:
in.devcoftb.net
ie.devcoftb.net (Expert Mode)
is.devcoftb.net (Skyblock)

Europe:
in.devcoftb.eu
is.devcoftb.eu (Skyblock)