Partitioning of your hard drive(s) can be as trivial as creating just two partitions, one for swap and the rest for the installation and everything else--this is the Debian default and recommendation for new users. Or it can be as complex as creating many partitions for different parts of the system to use. An argument for creating multiple partitions is that filling up one partition won't impact on other partitions (which could be a problem if the system is unable to function properly because the disk is full). Also, corrupting one partition (although rare) won't affect another, thus it is good to keep the system partition separate from the user partitions. Finally, having all user files (e.g., /home) on its own partition can mean that you can reinstall the operating system without wiping out the user files. The decision is yours.