On Mac, you can install a software downloaded from a web site or from a CD or a USB stick. All that you need is the .dmg or .pkg file that is supposed to install the software you want.
Take care however to make sure that the softwares you install can be trusted, otherwise they could contain virus (see protect a PC from virus
See also download a file if you wish to download softwares on the web to install them. (soon).
- Double-click on the dmg or pkg file to install.
- Follow the instructions or drag the software in the Applications folder.
- Your software is installed. If you click on the Finder and click on Applications, you will find your software there that you can also drag and drop in the dock in case you want to be able to access it easily.