Many web sites are devoted to provide software downloads. Some of them will offer freeware (software that you can use without paying), shareware (software that are free to share and tryout, but require registration after some time), and others are demo software and trial software, which serve as a demonstration of the software capabilities, but do not include all the features the full version has.
Whatever software product you are looking for, there is a big chance that you will be able to find freeware downloads that may be suitable for you, but have in mind that free software often comes without technical support (in fact, many of these free programs do not even include a help file!), so you may end up with an application that you cannot use.
Better choices are shareware and trial or demo software systems, generally built by companies instead of freelance programmers; these companies pay special attention to average user, including complete help files and customer support.
But no matter what software you need, you must choose serious sites from where you could download them, because there are many unsafe sites that will spread virus, spyware or other threats by making them appear as useful programs.
Another way to download software is by using a p2p program; while these sharing p2p networks increase the chances to find that program you need, they also (greatly) increase the risk of being infected by a dangerous virus or Trojan embedded on an apparently safe download. Furthermore, there is a chance that you will download software that is not free to use or even install, and therefore you will be breaking copyright laws without even knowing it.
But do not be scared by these words, I