You can back a project either by selecting one of its rewards, or by tapping on the floating "back this project" button on the footer. We continue with the button in the footer.
Now we need to select our reward, if we want one.
Now we select our payment method. We can use Apple Pay, or pay with a credit/debit card.
Our pledge has been made. We're prompted to share this using a Facebook or Twitter button. There's also a "More" button for more sharing options.
Under the share options, there are a couple of related projects we can check out.