The word mandala means "circle." Mandala's often have radial balance. For me I use mandala's to help improve my concentration and to relax.
I have noticed that it helps me to reduce stress levels to a lower level and sometimes get rid of it all together. Shapes and patterns of mandala's are added to a clearly calming center point. It is said that they are healing mediums for the soul and help with merging the body, spirit and soul.
It's all about what you believe it to do and how it may help you as a person. For me it does help me a lot when I'm working on them. They help to uncover inner creativity, to discover the real you from inside and to calm.
The three mandala's I posted were done by me at different times with my mood being different each time. I'm working on a couple of more but they are unfinished at this time and have been for awhile. LOL :P
This is the book I bought that I got the mandala's from.