By default, whole the macro text is executed by the macro engine.  This means that macro engine takes the macro text and considers it as a set of keystrokes to be sent to currently active window (target window).  This is very handy for macros that consist (mostly) from text to be inserted to a target application.  For example, let's have this macro:

Hello,
  thanks for your e-mail.

This macro, when played back, will insert the above too lines to the target application.  This allows users to create this kind of "text expand" macro simply by just typing required text in macro editor.
From other hand, there are also macros that do something that has nothing to do with inserting text (sending keystrokes) - file operation macros, download/upload from/to internet, changing registry, and many many other.  For such kind of macros it is not convenient that each new line (Enter key) is processed since it might affect the macro execution.  For this reason, there is <cmds> command.  It causes that only commands (for example, <filecopy>, <ftp_putfile>, etc.) are executed and all other text is ignored.  The opposite command is <keys> command that switch macro engine back to default behavior, i.e., all the macro text is executed (including new line interpreted as an "Enter" key).

Control Keys

Normal keys (like A-Z, 0-9, Page Down, Tab, etc.) are sent by macro engine as key ôpressö and key ôreleaseö sequence.  Control keys (e.g., Alt, Ctrl, Shift, etc.), that changes keyboard context, are different.  The first occurrence of such key in the macro has meaning "press key down" key and the second occurrence has meaning "release" key.   This means that, for example, "Ctrl+K" keystroke is represented as "<ctrl>k<ctrl>".

Some keys (for example, right Control key, or NumPad Enter key) are so called ôextendedö keys.  To simulate extended key keystroke use <extkey> command before the key.  For example, <extkey><newline> sequence has the same effect as pressing NumPad Enter key.