I've not got Sky, so I can't compare the way it works with their remote. To me, it's similar to the way that people with high scores enter their names on machines in video arcades.
i.e. you've got the alphabet displayed on the screen and you move the cursor right or left to the first letter you want to enter and press OK. Then you do the same for the second and so on.
However ('cos I've just taken a look at it) there's also a faster way of searching by using your mobile device or laptop after entering your box's pairing code here:
https://www.youtube.com/pair
If you've got a Youtube account (where, perhaps, you've stored all your favourite videos) you can log into it via your Now TV box and access those videos from the list you've got stored.