Many carriers that offer data plans have data usage monitors on their web sites. You can login there and check your data consumption.
There are apps you could use for monitoring your usage data.
You could also go to Settings - General - Usage to view your data on your iPad.
Yes you can check on your Carrier site for your data consumption used but be aware that many of these are not updated in real time.
I prefer to reset my statistics according to when my cellular data contract begins. Settings - General - Usage - Cellular Usage.
The IPad Forum is a community of members from all walks of life and from all over the world coming together to share our experiences and to help each other learn about this wonderful piece of technology the Ipad. There is a wealth of information already here in the many threads we have so doing some searches will answer most of the questions you have. If then you cannot find the answer you are seeking then by all means post your question. There are many friendly and informed members here only too willing to help you.