“make” just follows a recipe in the “Makefile”. Usually that recipe is to compile from source code format into binary format. The binary format is the executable. Now if it turns out that the binary was already somewhere in your default execution path, then you wouldn’t have needed to use “make”. This certainly wouldn’t have hurt. Mostly those examples are for people who want to see a source code example of how to do certain things, and thus if these were presented only in binary format, then this wouldn’t actually help in seeing how the source code is set up.
“make” can have different targets. The “-j4” just says to use 4 CPU cores during build…if you had 6 cores, then you might use “make -j6”.
“make” with no targets (and “-j4” is not a target) just executes some default recipe. Often there is a “make install” target (“install” is a target), and this would place the executable somewhere more “standardized”. Usually “install” requires root authority, so it’d be something like “sudo make install”. If “make” had not already been run, then “make” would have been executed, followed by “install” (it is hard to install what doesn’t exist, so “make” will test if the binary executable exists prior to trying to copy it to an install location).