Supermoon happens because the distance between the moon and Earth varies continuously because of its slightly elliptical orbit around Earth. It appears bigger than usual when it is at the point closest to Earth (up to 14% bigger compared to its furthest point away according to NASA) and when that happens, it is call "perigee-syzygy" (Supermoon is fine, even wiki uses that term... see here for technicalities)
No worries at all if you didn't see it in July, I didn't know about it either so I missed it too (hence no photo to show in this post, apologies...) BUT! There is another one coming up on the 10th August, at 11.25pm (UK time) and the moon will look even bigger compared to the last Supermoon! Thanks to the moon becoming a full moon within an hour of reaching its closest point to Earth in its orbit. So it's like the mother of all Supermoons.
Go write this in your diary/set a reminder on your phone/ask your friends to remind you, it really is something not to be missed. I will be trying my best to get photos too!
Best of luck with the weather for those in the UK! *fingers crossed*
Source - http://www.telegraph.co.uk/science/science-news/10966962/Super-duper-moon-expected-in-August.html
PS. Blog post about the Perseids meteor shower coming soon! (spoiler: the meteor shower's activity peaks round about next week, just after mother of all Supermoons)