How do I...PLEASE I want to insert in my database with a function

CREATE FUNCTION F_All
	(
	 @tache int,
	 @IdEtud int,
	 @Nom varchar(20),
	 @Postnom varchar(20),
	 @Sexe varchar(1),
	 @Tel varchar(20)
	)
	returns varchar(100)
	BEGIN
	Declare @request AS varchar(100)
		if (@tache=1)
		begin
			select @request=INSERT INTO tEtudiant (Nom,Postnom,Sexe,Tel) VALUES (@Nom,@Postnom,@Sexe,@Tel)
		end
		else if (@tache=2)
		begin
			select @request=UPDATE tEtudiant SET Nom=@Nom,Postnom=@Postnom,Sexe=@Sexe,Tel=@Tel WHERE IdEtud=@IdEtud		
		end
		else if (@tache=3)
		begin
			select @request=DELETE FROM tEtudiant WHERE IdEtud=@IdEtud	
		end
		else if (@tache=4)
		BEGIN
			select @request=SELECT *FROM tEtudiant WHERE IdEtud=@IdEtud	
		END
	RETURN @request
	END