Assignments:
There are two basic types of assignments--online and offline.
Here is a flow chart of how assignments work in Moodle.
flowchart
Directories:
Directories can display files. It's a good idea to setup a file structure for a course early on, even if you don't display directories. Otherwise your course documents might start looking like your desktop
Directory of Course Files for Blended Moodle
Activity: Watch Atomic Learning Tutorials
Task: Create Assignments in Your Moodle
Task: Create File Structure for Course
Forum: Assignments in Moodle