Channel
A channel is the entity who owns content, this could be something the channel posted themselves or another channels has taged them.
Project (CMS)
You can think of a project as a folder filled with assets and details about what the assets are, who has access, how do assets related to each other and so much more.
Assets
An assets represents a fils in storage or a pease of content (e.g. an audio file, a translation text, etc)
folder
group of assets