No question that you don't know the answer to is stupid. That is why we have this place.
A decant is actually a bit larger than a sample. It is a way to redistribute fragrances in smaller containers for things like travel, sampling (not the noun 'sample'), and sharing fragrances. Samples are in 2ml vials and are good for just a few applications. Decants start at 5ml sizes and are good for many applications.
This is a great site to find the many ways a decant can look and work: http://www.essentialsupplies.com/
Unfortunately selling decants here has been banned as a result of the ease a person selling a decant can manipulate the contents to make profits. They do cost money, but samples from a store usually do not. They try to promote the fragrances so they'll give you some freebies. Online vedors will charge you about $2 a sample usually.
For some clarification, samples are samples, decants are decants. You may sample frgrances with decants made by a friend but they are still decants.
Hope this helped!