The macros window allows you to see named values defined by plugins (or manually by the operator) which can be substituted into APRS text messages, beacons, status messages, and some other packet types which can be generated by plugins.
The general form for inserting a macro value into a APRS packet is for the free-text comment to contain text of the form
{M:macroname}
where macroname is the name assigned to the macro. This text will be replaced with the currently defined value of the macro. Some packets can also insert values from other sources, using formats like
{WX:temperature}
for inserting weather data into the packet in human-readable form. The user interface for editing the packet type will list the available macros that can be inserted, usually as buttons that will insert the appropriate macro reference at the current cursor position in the text editing field.