This is the modpack me and my friends are using to play on our modded Minecraft server.
If you already have the mod profile installed, download the mods.zip file. Extract its contents and add them to the mods folder found in your profile on twitch. The mods folder of your profile can be found by opening the twitch profile and clicking the gear in the top right corner. Click "Open Folder," then navigate to the mods folder. Add the mods to the folder and start Minecraft.
If you do not already have the mod profile, download the stuiff-x.x.zip file. Go to the twitch app and find "create custom profile." Click it and then click on import. Find the stuiff-x.x.zip file in the browser and open it. The pack will begin installing.