Once you've downloaded the installer you run it to carry out the actuall installation. This is often as simple as double clicking on the installation file. Once the installer is running, you will step through several dialogs, that may ask you to accept a license, select a maximal memory to use for the software, and select an installation directory. If you are upgrading to a newer version of NMRViewJ or dataChord you should not install the new version on top of the old version. Either remove (or move) the old version or install to a different location. On versions of Window's you should be able to find an Uninstaller program to run in the NMRViewJ or dataChord section of the start menu. Following are a few tips for different operating systems.
Simply find the installation ".jar" file in the Finder and double-click on it. The installer will start up and prompt you through the various steps of installation. The default installation will place NMRViewJ in the /Applications folder. After installation open the /Applications/NMRViewJ folder and find the NMRViewJ application. It has an icon like this:
The Mac should recognize ".nv" files as belonging to NMRView. If you double click on one it should startup NMRView (if it's not already running) and then display the file in a window.