"A macro is a set of commands that can be played back at will to perform a given task. These tasks can be something simple from inserting your name and address into a word processor to something more complex such as launching a program, copying data from it, activating another program, pasting the data into it and repeating this several times. Tasks performed by macros are typically repetitive in nature allowing significant savings in time by executing the macro instead of manually repeating the commands."
Microsoft Word allows you to make custom macros. There are other programs that allow macros as well. Some websites may enable or disable macros when you login.
Keyboard shortcuts (a key or combination of keys pressed at the same time) vary between programs. It all depends on the context. The context is either the specific task you are performing (like inserting text in the search box in Google), or the actual program you are currently
actively running. You are always running a program - even Microsoft Windows is a program. That means "control + S" might do one thing in one program and something else in another.
For example, type something into Google's search box and highlight or select it. Then press delete to delete the text. If you were to select a file, then pressing delete would have deleted the file.
In a word processor (like Microsoft Word), backspace will delete the previous letter, however backspace in a web browser (like Internet Explorer) will go back to the previous page - unless a text box is selected, in that case backspace will delete the previous letter.
In a word processor (like Microsoft Word), the tab key inserts a tab (a preset space, often used at the beginning of a paragraph). Tab in Microsoft Windows simply cycles through various things you can select (like the keyboard's version of a mouse).
In most programs, control + S will perform a save.
Here is a link to keyboard shortcuts for Microsoft products:
Microsoft Keyboard Shortcuts