You took my advice and got a Mac. Now what? This note is intended to be used with the help of an experienced Mac user, as a kind of guide to discussion topics.
Apple basic tutorials are at Mac Basics.
Lifehacker published a useful web page on how to Set Up and Get to Know Your New Mac, with lots of links, in 2012.
Read The Fine Manual that came with your computer. The Mac manual is very short, but useful.
Basic concepts (mouse, cursor, folders, etc) are well explained at Apple's Mac User Guide.
Use "Shut down" from the apple menu. (Don't just power the computer off; you can damage files.) Putting the computer to sleep is not the same as shutting down. See "Sleep and Shutdown".
To force a shutdown, if the computer won't shut down normally, hold the power key down for 10 seconds.
Applications are programs that run on your computer and do something for you. Many applications can be running at the same time. You tell what applications are running by looking at the Dock: the running applications have a dot below their icons. One application is "in front." It has its name next to the apple in the menu bar, and its menus are shown to the right of that. You can switch a different application to the front by clicking on its icon in the Dock. When you do this, the windows for that application come to the front.
Your Mac comes with a lot of applications. Apple has nice web pages about some of them.
The Finder is an application that is always running. It gives you a view of the files that are stored in your computer's file system. The Finder also lets you search for files. Type some text in the search box in the upper right and you will see a list of files containing the text; or type some text, choose "Name matches" in the dropdown, and you will see a list of files with that text in the name.
To dismount an external drive without damaging it, click the eject button (⏏) next to the drive's name in the Finder's left sidebar.
Make another app become frontmost.
Click on the icon for Safari in the Dock. It will open a window if your connection to the Internet is working.