Blender has gone back and forth on the merits of selecting with the left mouse button versus the right mouse button.
Recently the default was changed to be left click to select. This means that you'll find a mix of resources and tutorials each of which talk about selection slightly differently.
I've left in my argument (below) to switch back to right click select, but I've since given up on that argument and now accept the default of left click select. Luckily for you, any confusion will soon fade away as you use Blender regularly.
The Argument for Right Click Select#
Read this short article on why you should setup Blender with Right Click to Select:
|Right Click to Select.|