Assignments are common activities in Moodle. They will be designated by the icon. Depending on your instructor, an assignment might be a document that you need to upload(common) or it could be a text field you are to type in within the assignment(less common.) In most cases an assignment will accept all file type submissions, but please pay attention, your instructor can limit this to specific file type. For example they could limit it to a .doc, which would be a Microsoft Word document or they could specify they want documents converted to a PDF.
Once your Professor has graded an assignment they can leave you feedback in the form of a comment or they can add comments to your document and re-upload it for you to review.
Below are instructions for uploading assignments in Moodle, as well as reviewing feedback from your instructor.
Submitting an Assignment 
From the course page click on the assignment name to enter the assignment.
Review your professor's instructions
In the middle of the screen you can review the status of the assignment, If you have submitted yet, if the professor has graded it, the due date, and time remaining to submit.
When you are ready to proceed click "Add Submission"
If your instructor has added file limitations you will find them under "Accepted file types" if this area is blank all file types are acceptable.
Files can be dragged and dropped into the dashed box.
Or you can use the file picker by clicking on the icon.
From this screen you can choose several options for getting your document. "Server files," allow you to find files from your other courses, "Recent files" would be the last 30 files you have uploaded, "Upload a file," is used for finding files from your computer, "Private files," is your private moodle cloud storage space, "Wikimedia," is a private cloud driver, and "Google Drive," will connect to your google drive. The last two the first time you use them you will need to connect to your account.
For this tutorial we will click on "Upload a file"
Click on Browse
Viewing Assignment Feedback 
Scroll down to feedback
Once your assignment is graded, you will receive an email informing you, that the assignment has been graded. To view your grade and feedback. Click the "Grades" menu item from your class's left hand navigation menu.
This will take you to your gradebook. There are many ways that your instructor can set up the class gradebook. This example is a common gradebook set-up.
Scroll down to your assignment. In this example the first column is the weighted percentage that that grade is toward it's category at the time you look at it. In other words for this example our Assignment #1 counts towards 100% of our Assignments total grade, however it is the only item graded in this category and this number will change when more assignments are graded.
The second column in the points you were given for the assignment, and the third column is the total possible points. The fourth column is your percentage grade.
Click on the assignment name for more feedback.
Feedback comments are for general feedback on the assignment.
Feedback files will have more details on your assignment. Your Instructor can upload your documents with inline comments. They can also attach a grading rubric. Click on the file to download and view the feedback.