We recommend using MultiMC to download FTB Revelation. You could also use the Twitch launcher.
Once downloaded, click "add instance" in the upper left corner.
After, there will be a box on the left with some categories. Click on "FTB Legacy" to pull up the list of FTB based packs. We use the one called FTB Revelation. Select that one and then click on OK.
And that's pretty much it, the modpack should begin downloading. Once you're up and running, add our address to your multiplayer servers list.