Deep down in the guts of the machine the carriage return returns the carriage and the line feed moves the
print head down one line relative to the paper. This would be on a movable printhead printer.
Translation to a computer monitor should be reasonably obvious.

Doing one without the other will not produce the desired results:

Just doing a line feed
                       would produce something like this.

Just doing a carriage return would cause the second line to be printed over the first. Depending on the OS
and the keyboard hitting the return key will generate one, the other or both and the OS will fill in anything
missing to produce the desired result.

Or something like that.