Do I need a (valid) software license?

When you want to install a software program like Windows on your computer, then you have to accept the license terms they state (on the screen or on the cd). And you can not just say Yes, you must also follow the rules they set. One of these rules is “you may only use this software if you have bought an official copy.”, and another rule is “you are not allowed to copy the software”. These rules are set because the software companies want to make a profit on the things they produce. They can only make a profit if they sell a whole lot of copies, because creating a program like Windows takes an incredible effort. If people would just copy the software themselves, then the author would not make any money, and software writers would run out of a job.