Big and Large

  What's the difference between  big and large ?  Both they are adjective. 
I reference much information but I still can't figure out it.
It is very difficult to definition they.  We usually use a phrase " a  large amount of  " and
" a large number of " and then plus number. I think it' depend on you describe somethings.
We need reading much article and you will get rules. Soomeday you make a sentence
which is the best choice by natural.