1. You want to download the FTB app, you can find it for whichever platform you intend to play on
here.
2. In the FTB app, you want to press "browse", it should be the third or fourth icon down on the top left side of the screen.
3. You want to type in the search tab "Infinity", after you'll want to press the green download icon that corresponds with the "FTB Infinity Evolved 1.7" modpack, don't install the skyblock version.
4. After the modpack has finished installing, you can launch it by pressing the "library" icon, which is one icon above the "browse" icon, and hovering over the FTB Infinity Evolved modpack icon. [NOTE: the modpack is very large, and sometimes has trouble installing, if it crashes after launching a few times, try reinstalling the modpack]
5. After launching, you'll see an altered minecraft main menu screen, press "multiplayer"
6. Press "Add server" and type "mc.sipdns.net" into the box labeled "Server Address", you can put whatever you want in the box labeled "Server Name"
7. After typing in the correct information you should see a screen like this
8. Select the server, and press "Join Server"
9. Have fun