You browse at Warby Parker Free Home Try-On's selection pages. You add them to your cart and at checkout pay a $1.00 fee. That is their way of being able to charge you if you do not return the frames in 5 days. They ship them to you in a very sturdy box. You then have 5 days to try them on and get peoples opinions and form your own!
If you love a pair, you can keep them and be charged for them.
Or you can send them back and purchase them online at a later time.
When you send them back you just put on the prepaid label on the box