Understanding docker

I want to make sure that I understand docker correctly here. My principal goal is to distribute little pieces of software (usually with full source-code) I write in Python/Haskell or C++ to my friends and colleagues.

I myself work on an Ubuntu 14.04 machine. But often the people whom I distribute it to work on different machines and operating systems and they don't have the libraries needed to run my codes.

If I understand docker correctly, is the following a valid use case?

• Set up an empty docker folder
• Write code and install all the libraries and dependencies in that folder.
• Upload it to the docker cloud
• Tell my friend to download it on his Windows machine or Mac and run the code without any fuss.

Is this a good summary of what docker allows? If so that is fantastic news, since it will help me a lot in making my research work reproducible and distributable across multiple machines.

I don't really understand the explanations online when they compare this software against virtual machines.

- - , .
.