Hi Charlie,
Here's how to do it.
When you're in Edit on your About page, highlight the words first. In your case, highlight "www.charliewhitfield.photography"
Put your cursor on the highlighted words and right-click them (I'm pretty sure it's a right-click. On my laptop, I use two fingers to tap the touchpad).
A menu should open. Select "Insert/Edit Link."
In the URL link field, enter "http://www.charliewhitfield.photography" and in the Target field, select "Open Link in New Window."
Then click Insert and Save presentation.
Hope that works for you.
Mandy