We all use internet on our Smartphone. It can be our 2G or 3G or Wifi. If we are on a limited network like using a mobile data plan which has a data limit then it is not so easy to track the usage. You can try using third party application which can be in accurate. But Moto X and many other android phone that has Kitkat update comes with a internal settings through which you can track the Data Usage. You can easily find out which application in the device is consuming the amount of data. You cannot limit the data usage but you can see on which day how much data is downloaded. If you have a 1GB or 2GB limit or if you are paying for each download, then through this you can restrict your usage. You have to check there manually. It is a effective solution to keep your data usage under check.
For that just Tap on Settings and then look under Wireless & Networks.
Tap on Data Usage. at the top side you can see a graph of your data usage and below you can see the it of applications. You can scroll down to get the whole list.
To find information about a specific app tap on the same. For example Google Play Store. A new screen appear with pie chart and you can see how much data its has consumed.
You can find date wise information about data consumed. For that you have to tap on the date on the top next to Date Usage Cycle. You can find this information for each and every app.
Along with mobile network you can track data usage for mobile hotspot also. Just tap on the three dots on top right and select the wifi or hotspot from there.