Syntax in a NSIS script file

Due to usage of the NSIS Logic Library (implemented by the command
"!include LogicLib.nsh" in the *.nsi sript file) I often encountered constructs, which contain the 3 characters "$", "{" and "}".

Typical examples are:

• ${If}
• ${EndIf}
• ${FileExists}
• ${WordReplace}
• ${SetEnvironmentVariable}
• ${SegmentOnit}
• ${SegmentPrePrimary}

But in which cases is it necessary to use these characters and why I can omit these characters in connection with the following instructions:

• CopyFiles
• WriteINIStr

It just means insert the content of a define

!define xyz "OhCrap"
!error ${xyz}

A common way to create helper functions is

!define MyFunc "!insertmacro MyFuncImplementation"
!macro MyFuncImplementation
DetailPrint "Performing myfunc"
Exec '"myfunc.exe" /w00t'
!macroend

..and call it with ${MyFunc}. Other functions like CopyFiles are native functions that makensis.exe knows about and they are documented in the main helpfile...