how to get new apps on this computer

Applications don't have to come from the App Store. You can navigate to a companies website (ie: Firefox) and download a Firefox installer. It will appear similar to how you mentioned it above: firefox.dmg. You open that file from your "Downloads" folder, and it will install the application on your computer.

Shop for them by opening the App Store in your Applications folder or clicking on its icon in the Dock. Sign in with your Apple ID and password. There are tens of thousands of apps - some free, some not free. You can also visit the:

How To Safely Use MacUpdate To Download Ad-Free Software

This site has both free and paid membership accounts. If you have neither then some software will be distributed as an installer wrapper that includes adware/malware you may not want. Such a download may appear on your computer like this: Firefox Installer.dmg. Delete the download and return to the main site where you will find a direct link to the developer's website. Use that link from which to download the software. Or a simpler way is to establish a free or paid membership to avoid problems getting adware with your download.

Then I must ask you to correct your English. To say, "download from Safari," implies/means that Safari is a place like the App Store. To say, "download using/with Safari," implies/means use Safari to get an app from a place. Safari or Firefox or any other browser downloads files to your Downloads folder.

In fact, as I remember things firefox.dmg does not install Firefox. It opens a window with the visual suggestion to Drag Firefox from the mounted disk image and Drop the file in your Applications folder.

Apologies if this seems a bit pedantic but the language can often mean something different than what is in your head at the time you write it out.

Open up the App Store application in your "Applications" folder. From there, you can download apps. You can also download third-party applications from Safari.

Forgive me for sounding dumb, but how do you download applications from Safari? I thought Safari was a browser, not an app store. Please educated me.