How can software be free?
There happens to be a great deal of software out there that is available at no charge. These are usually called freeware applications. There is another kind called open source software. There are others that have varying degrees of "freeness" based on other conditions, such as being free for home users but not corporate users. How can it be that so much software is free?
Individual programmers and entire companies produce these gems for your use, without requiring you to pay anything. Even Microsoft does this. It makes good business sense, because the more people that use your product, the more your brand name will show up on the end users computer. Also, some people are altruistic, and creating software for others gives them a sense of accomplishment. There are those out to prove that the commercial world doesn't produce the best software. The Open Source community has long held beliefs about sharing software code for everyone to benefit.
Free software can install hidden malware. You can find free software at many places, but be wary and find trusted sites, like BleepingComputer.com. Some of the software you'll find on there is not free, but still useful. Their website is also full of tips on how to deal with viruses and other malware. It's a great resource for troubleshooting your computer problems.