A blue moon occures when there are 2 full moons in the same month. It's basically like a regular moon though some claim it's more connected with divination or the wisdom of the Goddesses Crone form as well as dedications and goal setting. However, it's just an extra moon, if you need to bless a new deck of tarot or were planning a spell to help you with a goal [money spell to help visit Paris, weight loss, quit smoking] you'll have better odds, but it's another full moon to celebrate. I personally like that it falls on Lughnasadh/Lammas I like when holidays also have a full moon.
I simply see it as another full moon. Since our modern calendar is not lunar based I see nothing special about there being two full moons in the same month. All full moons are good for banishing unwanted influences (since, from this point to the new moon it is waining), shining a light on issues or challenges, protection and divination work, releasing old patterns or issues and healing by getting rid of what doesn't work anymore. It is also the full moon in Leo, which means it is good for working with issues of power over others, courage, strength and any of the qualities governed by Leo.