Android operating system already provides the ability to see what apps are using data from your cellular network, but the information is basic. To get a better picture of what apps are really using your mobile data and when, I recommend GlassWire. It is available for free in Google Play Store.
It shows nice graphs and you can see exactly how much data your apps have consumed and when. You will see exactly at any point what app consumed the most data. In this way, you can manage your data consumption and avoid overcharges.
All the information is packed in nice timed graphs. This is the best feature of this application, along with the very nice and modern interface.
Another nice feature that you won’t find in other apps is that it allows you to ignore data usage for certain actions, for example watching youtube videos or browsing facebook, that you Inernet Service Provider is giving you unlimited amount of traffic. This is against Net Neutrality, because they favor some websites or content over others, but carriers around the world are using it with no regrets.
You can download GlassWire from Google Play Store.