The easiest way to get graded work back to students is to create your course with "Student email support" enabled. When this is checked, the site will ask students to enter their email addresses when they upload their essays.
Alternatively, you can manually enter their info, but it's much easier to just let the site build your roster on-the-fly as students submit their essays.
Then when you're done grading an assignment, you just click on the "email graded work to students" tab on the assignment details page. Follow the instructions and the site will email each of your students a personalized link to their graded essay. Students will not need a login or password; the links are already encrypted and only someone who receives the link can access the graded essay.
As a fallback option, you can also print the graded essay or copy-and-paste each student's link to their graded papers.