Could anyone help me out to find the difference between salt cellar and salt shaker? and which one the most used in the USA??
I disagree. 'Salt cellar' is the UK term for 'salt shaker' (AE).
See the Cambridge dictionaries, I quote:
UK (US salt shaker)
small container for salt, usually with one hole in the top
Oxford Dictionaries, I quote:
A dish or container for storing salt, now typically a closed container with perforations in the lid for sprinkling.
It used to be only a pot with a lid, but now includes what AE speakers call a "salt shaker".
I've never heard of a salt cellar before at all. Because a "cellar" is a storage room in a basement, it had me thinking of a room full of sealed salt containers waiting to be used to replace the one that's actually being used in the kitchen upstairs when it's empty... which sounded weird because nobody needs enough salt to dedicate a whole room to it, so no such rooms actually exist, but there was nothing else I could think of that fits the word "cellar".