Installing a Software: Guide
In order to install a software, you usually need a product key which comes with it. If your software doesn't come with one and you are asked for a key while installing, be sure to contact the seller. You can also find free softwares online but they usually are trial versions, which expire after a certain date.
Extending a Trial Version: Tips
An easy way to keep the trial version running is to uninstall it and then re-install the software to extend the expiry date. For example, a trial is offered for 30 days. If you will uninstall and then do a re-install, it will give you 30 more days. This trick has been used by many people and still works.