Landscape fabric pins, or "garden staples" can be inserted through the weed barrier to pin it down. The pins are usually sold separately from the fabric.
No need to go crazy with the landscape fabric pins; remember, the mulch will help hold the landscape fabric down, too. A landscape pin every ten feet along the exposed edges (and along seams, where you have overlap) should be sufficient.
Now that the landscape fabric is secured, apply your mulch on top of it. Using the steel rake, spread it out evenly.
On Page 8 I'll talk about cutting into your landscape fabric in order to make planting holes.