You can choose to set up a subscription when you are on the product page or in the shopping cart.  

Once you are on the product page, it will initially be set to "Subscribe & Save". You will see a drop down menu for you.

Click on the arrow and select the frequency with which you want the product to be delivered. Don’t worry, if you find that you want to amend the frequency at a later date, then you can change this under Manage Subscriptions on the footer of the website.

Once you have selected your frequency, click on "Add to cart" to proceed to checkout and place the order. Your product will now be dispatched at the frequency requested.