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)
Install the pack (You don't need to add any additional mods)
But unselect Chat Flow mod. It can cause crashing and Devco has it's own alternative for your enhanced gameplay.
Click Launch to launch SkyFactory
We are currently running the version listed here