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The FTB team have created a great launcher utility that makes it easy to install their modpacks. Just hit up their website and choose "Download Stable" to get the launcher. They also have a wiki with lots of info if you get stuck or just want more information.
Once you have the FTB Launcher open select the "FTB Modpacks" tab (it is probably selected by default). In the list of modpacks on the left choose "FTB Infinity Evolved 1.7 (v2.4.2)" which should be the first in the list. In the lower left there should be a dropdown between the "Edit" and "Launch" buttons. Click on that and create a profile with your Minecraft/Mojang user info. Finally hit "Launch" and the FTB Launcher will download all the mods and set everything up.
The "Options" tab in the FTB Launcher lets you change the install location and how much RAM is allocated to Minecraft if you want to tinker but the defaults should be fine.
After you have launched Minecraft at least once with the modpack you will need to then exit out and download this zip with the extra mods. Put the files in that zip into the "mods" folder in your minecraft install location.
As is usual with any version of Minecraft, it is a good idea to make sure your version of Java is up-to-date and you have the x64 client if you have a 64 bit CPU.
Once you have Minecraft up and running with the mods go to Options -> Controls and set up all the new keyboard commands. Any of the commands that show as red in the list have more than one thing mapped to the same key.
After you've launched Minecraft with the modpack at least once (so all the mods are downloaded) you can add any optional mods you want via the "Edit Mod Pack" button on the "FTB Modpacks" tab. These are usually just eye candy for making Minecraft look a bit fancier. I have provided some links below if you are interested.