How to put an object in a room using an If statement

I’m just starting my first Inform 7 project.

I want to put an object in a room when you open the window (something flies in).

I’ve tried various things along the lines of:
[if opening window for the first time] Put the flies in the Living Quarters[endif].

Can someone tell me how to actually put an object in a room if an action occurs for the first time?

After opening the window for the first time: 
	now the fly is in the location;
	say "As you open the window, a fly darts in."

Thank you! You’re a life-saver. I can see I was struggling with the use of “now”, which I didn’t think to combine. It’s gonna be uphill for a while, but I do think it’s a great “language” to work with.