This will vary from class to class and in most cases any additional software that is required for a specific class will come with your textbook.
It is recommended that students use Microsoft Word for most writing assignments unless otherwise specified by the instructor. The college bookstore carries the student edition of Microsoft Office which is a version of Microsoft Office discounted for student use.
For students taking the Intro To Computers course Microsoft Office Professional 2010 is required to complete assignments.
Many instructors create their documentation in PDF format. Fortunately, the program you need to view these files is free to download. Download Adobe Reader XI directly from Adobe.com.