The simplest way to get started with open source software applications is to use a search engine such as Google to search for “open source” and the name of type of application you’re interested in (for example, “open source database”). This will give you a list of any open source projects developing applications in that category.
Look over the list and click on the websites of any projects that seem to fit your needs. Read at least the beginning of the overview of each project to get a better idea of whether it’s what you are looking for or not, and if it seems worth trying, find the “download” link and download a copy of the current release. Remember that if an application is indeed open source, it will be free to download (although a donation to the project may be suggested) and back versions will be available as well as the current release. You’re likely to encounter fewer problems if you select the most recent stable release rather than the current beta test release.
Try installing the application. Be alert for messages about insufficient disk space or an unsupported operating system version. If installation is successful, try out the application see if it is suitable for your purposes.
You may have identified several applications you want to try. If so, repeat this process for each one. It may be helpful to take some brief notes on each candidate application as you experiment with it.
With luck, you’ll have found one that does exactly what you want, in which case you’ve added an open source application to your arsenal! If not, you’ve probably learned some things that can help you evaluate commercial applications in that category more knowledgeably.
When you’re finished, uninstall any applications you’ve tested and rejected to avoid clutter.