Depending on how it was installed, sometimes there's an uninstaller if it used an installer to install the program. Other times, if the application was just dragged over from a disk image, all you have to do is drag it out to the trash and empty it.
Usually, the latter is a well-behaved Macintosh app. That's the way it's always been done since day one. We can thank Microsoft for making installations and uninstallations as painful as they are now.
For most OS X applications there are two and possibly three files to be deleted
The application file itself (which is actually a special kind of folder and my include over a thousand bundled files.
The preference file which is found in your home folder ~/Library/Preferences. By standard the preference file will have a name of the form com.pppppp.aaaaaaaaa.plist where pppppp is the name of the publisher and aaaaaaaaa is the application name. For example com.apple.safari.plist. Unfortunately not all developers follow the standard so this may take some looking to find
A few applications will create a folder in /Library/Application Support or ~/Library/Application Support
Applications that install drivers into the system almost always have an uninstaller either built into the installer routine or as a standalone script that comes with the application. If an application is installed using an installer, it should be removed the same way.
If you run into a situation where your uninstalled apps you moved into the trash won't delete, it is because they running and the cure is to restart the Mac then empty the Trash.
ie, they won't start at login if they are in the trash and the system won't be running the apps plugins or what ever