1) Document Library can have Check in/out feature, but a custom list does not have this feature.
2) When particular item is getting added to a document library then it must be a file. You can't have a library without a file. Custom list doesn't have a file.
You can upload some document or content in a document library , which will be stored in the sharepoint content database. List is a piece of data same as that of SQL table.
I hope it will be useful for you.