One of the most useful features is the spelling and grammar check facility, since these types of basic errors will count against you. Word processing software makes it easy to set margins and tabulations, import tables and graphics, create a contents page and insert headers, page numbers and footnotes, all of which enhance the quality of your assignments.
With the cut/copy and paste facility, you can reorder your text to optimize the flow of information. You can also see exactly how your work will look before you print it out, so that you can check the layout. The formatting functions ensure that your work is consistent --- for example, heading styles and bullet points.
You still need to proofread your work, since the spell checker is not infallible. It will not pick up on spelling mistakes if the word you have typed actually exists: for example, if you typed "work" instead of "word."