"TemplateSelection" is a front end token that creates a template based on the currently selected function name.
This token is equivalent to the menu command Input Make Template.
This command reads your current selection (which should be a function name or insertion point after a function name) and adds a template for the arguments it can take. See Make Template for more information.
To execute a front end token, you typically evaluate a command of the form FrontEndExecute[FrontEndToken[token]].